diff --git a/apps/studio/src/test/fixtures.ts b/apps/studio/src/test/fixtures.ts
index c6b41066..100ab8e7 100644
--- a/apps/studio/src/test/fixtures.ts
+++ b/apps/studio/src/test/fixtures.ts
@@ -60,6 +60,7 @@ export const capitals: LibraryDeck = {
   keywords: {},
   title: { en: "Capitals" },
   cardCount: 3,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
diff --git a/apps/studio/src/ui/CardWorkbenchContainer.test.tsx b/apps/studio/src/ui/CardWorkbenchContainer.test.tsx
index 3662abeb..20d7f754 100644
--- a/apps/studio/src/ui/CardWorkbenchContainer.test.tsx
+++ b/apps/studio/src/ui/CardWorkbenchContainer.test.tsx
@@ -207,6 +207,7 @@ describe("CardWorkbenchContainer", () => {
       ...firstRelease(url),
       title: { en: "Solid" },
       cardCount: 1,
+      languages: [],
       authors: [],
       direction: "front-to-back",
       sources: [],
diff --git a/apps/studio/src/ui/DeckTableContainer.test.tsx b/apps/studio/src/ui/DeckTableContainer.test.tsx
index 23a82d7f..612937f0 100644
--- a/apps/studio/src/ui/DeckTableContainer.test.tsx
+++ b/apps/studio/src/ui/DeckTableContainer.test.tsx
@@ -150,6 +150,7 @@ describe("DeckTableContainer", () => {
       ...firstRelease(course.sourceUrl),
       title: { en: "Solid" },
       cardCount: 5,
+      languages: [],
       authors: [],
       direction: "front-to-back",
       sources: [],
diff --git a/apps/studio/src/ui/GroupsContainer.test.tsx b/apps/studio/src/ui/GroupsContainer.test.tsx
index bafa4313..40fbef0c 100644
--- a/apps/studio/src/ui/GroupsContainer.test.tsx
+++ b/apps/studio/src/ui/GroupsContainer.test.tsx
@@ -21,6 +21,7 @@ const solid: LibraryDeck = {
   ...firstRelease(RELEASE),
   title: { en: "Solid" },
   cardCount: 1,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
diff --git a/docs/deck-library.md b/docs/deck-library.md
index e00df1e8..a088a6b8 100644
--- a/docs/deck-library.md
+++ b/docs/deck-library.md
@@ -784,11 +784,28 @@ flowchart LR
   format-4 release's untagged keywords stay untagged, their language
   unknown. A series or release
   that does not fit its shape is left out.
-- The library screen lists each deck's name and card count with a
-  checkbox, filtered by **topic** (checkboxes of the topics the decks
-  name, a broader topic finding the narrower: "Languages" finds the
-  Swedish decks) and by a **search** of names, descriptions and keywords,
-  in every language (`filterLibraryDecks` in [domain/library.ts](../packages/domain/src/library.ts)).
+- The library screen lists each deck's name, card count and the
+  languages of its cards with a checkbox, filtered by **topic**
+  (checkboxes of the topics the decks name, a broader topic finding the
+  narrower: "Languages" finds the Swedish decks), by **card languages**
+  (checkboxes of the languages the decks state, a deck shown when its
+  cards are in every one checked) and by a **search** of names,
+  descriptions and keywords, in every language (`filterLibraryDecks` in
+  [domain/library.ts](../packages/domain/src/library.ts)). The checked
+  topics and languages and the search are kept until a reload, so a look
+  at a deck's page and back finds the list as it was left.
+- A deck's card languages are its current release's `dcterms:language`
+  (`LibraryDeck.languages`), read by `toLibraryDecks` from the index and
+  by `toStandaloneLibraryDeck` from a release added from a link: IRIs of
+  the EU's language table, in the order the release gives them, none
+  when it states none (the shape does not ask for them). Each is named
+  in the app's language with `Intl.DisplayNames`, through its language
+  tag ("KOR" is "ko", `languageTagOf` in
+  [domain/euLanguages.ts](../packages/domain/src/euLanguages.ts), which
+  tags every language `EU_LANGUAGES` lists); one not on that list is
+  left out. They are not worked out from the cards, which would mean
+  reading every release before the list can show. The row, the deck's
+  page and its preview name them.
   The search ignores case and Unicode form: query and text are compared
   composed (NFC), so "사람" or "é" pasted decomposed (NFD), as macOS
   file names and some PDFs hold text, still finds the deck; and Arabic
diff --git a/docs/user-guide.md b/docs/user-guide.md
index ffa15752..e1f2adc8 100644
--- a/docs/user-guide.md
+++ b/docs/user-guide.md
@@ -246,8 +246,10 @@ All of this is described in [browsing.md](browsing.md).
 ## The deck library
 
 **Deck library**, under the deck list, lists ready-made decks
-([deck-library.md](deck-library.md#in-the-app)). Search by name,
-description or keyword, or narrow the list to topics. Many of the decks
+([deck-library.md](deck-library.md#in-the-app)), each with the
+languages its cards are in. Search by name, description or keyword, or
+narrow the list to topics, or to the decks whose cards are in the
+languages you check. Many of the decks
 teach a language: Arabic, English, Finnish, French, German, Italian,
 Japanese, Korean, Portuguese, Spanish and Swedish. There are four
 Arabic decks: Basic Arabic and the most common nouns, verbs and
@@ -514,6 +516,7 @@ screenshot of each.
 | Grouping decks | full-learner | 09–11 |
 | Statistics, and a card's history | full-learner | 15–15b |
 | Previewing and importing a library deck | full-learner | 16–17 |
+| Narrowing the deck library to the language of the cards | [library-languages.journey.ts](../e2e/journeys/journeys/library-languages.journey.ts) | 02–04 |
 | Describing a deck in two languages, and switching language | full-learner | 18–20b |
 | Showing a deck's cards in another language than the app's, and back | full-learner | 20c–20d |
 | Checking the instance (developer mode) | full-learner | 21 |
diff --git a/e2e/journeys/journeys/library-languages.journey.ts b/e2e/journeys/journeys/library-languages.journey.ts
new file mode 100644
index 00000000..c6f83cb9
--- /dev/null
+++ b/e2e/journeys/journeys/library-languages.journey.ts
@@ -0,0 +1,49 @@
+// SPDX-FileCopyrightText: 2026 Anton Wiklund and Solid Memo contributors
+//
+// SPDX-License-Identifier: MIT
+
+import { expect, test } from "../fixtures.ts";
+import { BRIGHTEST_STARS } from "../pages/Library.ts";
+
+/** The one library deck whose cards are in Japanese (decks/index.ttl). */
+const JAPANESE_BASICS = "Basic Japanese";
+
+/**
+ * The deck library narrowed to the language of the cards
+ * (docs/deck-library.md, In the app): a guest checks Japanese under
+ * "Card languages" and finds only the deck whose cards are in it, its
+ * row naming its languages; its page names them too, and back in the
+ * library the language is still checked, until it is unchecked.
+ *
+ * What it catches: the index's dcterms:language not read, or read into
+ * names the browser cannot give (an EU language IRI with no tag), and a
+ * filter lost on the way to a deck's page and back.
+ */
+test("the deck library narrowed to the language of the cards", async ({ app }) => {
+  await app.step("01 · Visit Solid Memo and try it as a guest", async () => {
+    await app.onboarding.visit();
+    await app.onboarding.tryAsGuest();
+  });
+
+  await app.step("02 · In the deck library, check Japanese: only its deck is left", async () => {
+    await app.library.open();
+    await app.library.expectDeck(BRIGHTEST_STARS.en);
+    await app.library.expectRowLanguages(BRIGHTEST_STARS.en, ["English", "Swedish"]);
+    await app.library.checkCardLanguage("Japanese");
+    await expect.poll(() => app.library.shownDecks()).toEqual([JAPANESE_BASICS]);
+    await app.library.expectRowLanguages(JAPANESE_BASICS, ["Japanese", "English", "Swedish"]);
+  });
+
+  await app.step("03 · Its page names the languages of its cards", async () => {
+    await app.library.openDeck(JAPANESE_BASICS);
+    await app.libraryDeck.expectCardLanguages(["Japanese", "English", "Swedish", "Korean"]);
+  });
+
+  await app.step("04 · Back in the library, Japanese is still checked; uncheck it", async () => {
+    await app.chrome.breadcrumb("breadcrumbs.library");
+    await app.library.expectCardLanguageChecked("Japanese");
+    await expect.poll(() => app.library.shownDecks()).toEqual([JAPANESE_BASICS]);
+    await app.library.uncheckCardLanguage("Japanese");
+    await app.library.expectDeck(BRIGHTEST_STARS.en);
+  });
+});
diff --git a/e2e/journeys/pages/Library.ts b/e2e/journeys/pages/Library.ts
index 45862e2e..c2266233 100644
--- a/e2e/journeys/pages/Library.ts
+++ b/e2e/journeys/pages/Library.ts
@@ -68,6 +68,51 @@ export class Library extends Screen {
     });
   }
 
+  /** The decks the list shows, by name, in its order. */
+  async shownDecks(): Promise<string[]> {
+    return this.page.getByRole("main").locator(".library-deck-name").allInnerTexts();
+  }
+
+  /** A box of "Card languages", by the language's name in the app's language. */
+  private cardLanguage(name: string): Locator {
+    return this.page
+      .getByRole("group", { name: this.t("library.cardLanguages"), exact: true })
+      .getByRole("checkbox", { name, exact: true });
+  }
+
+  /** Checks a language under "Card languages": the list keeps the decks with cards in it. */
+  async checkCardLanguage(name: string): Promise<void> {
+    await this.intent(`Check the card language ${name}`, async () => {
+      await this.cardLanguage(name).check();
+      await expect(this.cardLanguage(name)).toBeChecked();
+    });
+  }
+
+  /** Unchecks a language under "Card languages". */
+  async uncheckCardLanguage(name: string): Promise<void> {
+    await this.intent(`Uncheck the card language ${name}`, async () => {
+      await this.cardLanguage(name).uncheck();
+      await expect(this.cardLanguage(name)).not.toBeChecked();
+    });
+  }
+
+  async expectCardLanguageChecked(name: string): Promise<void> {
+    await this.intent(`Check ${name} is still checked under the card languages`, async () => {
+      await expect(this.cardLanguage(name)).toBeChecked();
+    });
+  }
+
+  /** The languages a deck's row names beside its size: `names`, in the deck's order. */
+  async expectRowLanguages(title: string, names: string[]): Promise<void> {
+    await this.intent(`Check the row of ${title} names its card languages`, async () => {
+      const row = this.page
+        .getByRole("main")
+        .getByRole("listitem")
+        .filter({ has: this.page.getByRole("link", { name: title, exact: true }) });
+      await expect(row).toContainText(names.join(", "));
+    });
+  }
+
   /** Opens a deck's page (LibraryDeck) by its name. */
   async openDeck(title: string): Promise<void> {
     await this.intent(`Open the library deck ${title}`, async () => {
diff --git a/e2e/journeys/pages/LibraryDeck.ts b/e2e/journeys/pages/LibraryDeck.ts
index 22792f39..1fe509e5 100644
--- a/e2e/journeys/pages/LibraryDeck.ts
+++ b/e2e/journeys/pages/LibraryDeck.ts
@@ -26,6 +26,17 @@ export class LibraryDeck extends Screen {
     ).toBeVisible();
   }
 
+  /** The page's facts name the languages of the deck's cards, `names` among them. */
+  async expectCardLanguages(names: string[]): Promise<void> {
+    await this.intent("Check the deck's page names its card languages", async () => {
+      const term = this.page.getByRole("term").filter({
+        hasText: this.t("libraryDeck.cardLanguages", { count: 2 }),
+      });
+      const languages = term.locator("xpath=following-sibling::dd[1]");
+      for (const name of names) await expect(languages).toContainText(name);
+    });
+  }
+
   /**
    * "Copy link": the link to the deck that names no instance, as the app
    * wrote it to the clipboard. Only Chromium lets a page read the
diff --git a/e2e/pod/src/courses.integration.test.ts b/e2e/pod/src/courses.integration.test.ts
index 8b69e280..2717c103 100644
--- a/e2e/pod/src/courses.integration.test.ts
+++ b/e2e/pod/src/courses.integration.test.ts
@@ -116,6 +116,7 @@ const course: LibraryDeck = {
   keywords: content.keywords,
   title: content.title,
   cardCount: cards.length,
+  languages: [],
   authors: content.authors,
   direction: "front-to-back",
   sources: [],
diff --git a/e2e/pod/src/deckUpgrade.integration.test.ts b/e2e/pod/src/deckUpgrade.integration.test.ts
index e61a2634..12312a53 100644
--- a/e2e/pod/src/deckUpgrade.integration.test.ts
+++ b/e2e/pod/src/deckUpgrade.integration.test.ts
@@ -104,6 +104,7 @@ function libraryOf(...published: LibraryDeckContent[]): DeckLibrary {
         keywords: current.keywords,
         title: current.title,
         cardCount: current.cards.length,
+        languages: [],
         authors: current.authors,
         direction: current.direction,
         sources: [],
diff --git a/e2e/pod/src/guestTransfer.integration.test.ts b/e2e/pod/src/guestTransfer.integration.test.ts
index b8f7b62a..42567ce1 100644
--- a/e2e/pod/src/guestTransfer.integration.test.ts
+++ b/e2e/pod/src/guestTransfer.integration.test.ts
@@ -78,6 +78,7 @@ const course: LibraryDeck = {
   keywords: {},
   title: content.title,
   cardCount: 1,
+  languages: [],
   authors: content.authors,
   direction: "front-to-back",
   sources: [],
diff --git a/e2e/pod/src/metadata.integration.test.ts b/e2e/pod/src/metadata.integration.test.ts
index 0b863e9f..73b305ec 100644
--- a/e2e/pod/src/metadata.integration.test.ts
+++ b/e2e/pod/src/metadata.integration.test.ts
@@ -80,6 +80,7 @@ const course: LibraryDeck = {
   keywords: {},
   title: content.title,
   cardCount: 0,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
diff --git a/packages/application/src/testing/fakePorts.ts b/packages/application/src/testing/fakePorts.ts
index 2798a74b..5449c76b 100644
--- a/packages/application/src/testing/fakePorts.ts
+++ b/packages/application/src/testing/fakePorts.ts
@@ -82,6 +82,7 @@ export const libraryDeck: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals" },
   cardCount: 1,
+  languages: [],
   authors: ["Anton Wiklund"],
   license: "https://creativecommons.org/publicdomain/zero/1.0/",
   direction: "front-to-back",
diff --git a/packages/domain/src/euLanguages.test.ts b/packages/domain/src/euLanguages.test.ts
new file mode 100644
index 00000000..1af70d06
--- /dev/null
+++ b/packages/domain/src/euLanguages.test.ts
@@ -0,0 +1,29 @@
+// SPDX-FileCopyrightText: 2026 Anton Wiklund and Solid Memo contributors
+//
+// SPDX-License-Identifier: MIT
+
+import { describe, expect, it } from "vitest";
+import { EU_LANGUAGES } from "@solid-memo/vocab/concepts.generated";
+import { languageTagOf } from "./euLanguages";
+
+const LANGUAGE = "http://publications.europa.eu/resource/authority/language/";
+
+describe("languageTagOf", () => {
+  it("gives every language of the reference data a tag of its own", () => {
+    const tags = EU_LANGUAGES.map((concept) => languageTagOf(concept.iri));
+    for (const [index, tag] of tags.entries()) {
+      expect(tag, EU_LANGUAGES[index]!.code).toMatch(/^[a-z]{2}$/);
+    }
+    expect(new Set(tags).size).toBe(EU_LANGUAGES.length);
+  });
+
+  it("tags the table's languages by their two-letter codes", () => {
+    expect(languageTagOf(`${LANGUAGE}ENG`)).toBe("en");
+    expect(languageTagOf(`${LANGUAGE}KOR`)).toBe("ko");
+  });
+
+  it("has no tag for an IRI the reference data does not describe", () => {
+    expect(languageTagOf(`${LANGUAGE}NOR`)).toBeUndefined();
+    expect(languageTagOf("https://example.org/swedish")).toBeUndefined();
+  });
+});
diff --git a/packages/domain/src/euLanguages.ts b/packages/domain/src/euLanguages.ts
new file mode 100644
index 00000000..2f7a0302
--- /dev/null
+++ b/packages/domain/src/euLanguages.ts
@@ -0,0 +1,36 @@
+// SPDX-FileCopyrightText: 2026 Anton Wiklund and Solid Memo contributors
+//
+// SPDX-License-Identifier: MIT
+
+import { EU_LANGUAGES } from "@solid-memo/vocab/concepts.generated";
+
+/**
+ * The language tag (BCP 47, lower case, as the app keeps them) of each
+ * language of the EU's table a release may state (EU_LANGUAGES), by its
+ * code there.
+ */
+const TAGS: Readonly<Record<string, string>> = {
+  ARA: "ar",
+  DEU: "de",
+  ELL: "el",
+  ENG: "en",
+  FIN: "fi",
+  FRA: "fr",
+  ITA: "it",
+  JPN: "ja",
+  KOR: "ko",
+  LAT: "la",
+  POR: "pt",
+  SPA: "es",
+  SWE: "sv",
+};
+
+/**
+ * The language tag of a language of the EU's table, by its IRI
+ * (".../authority/language/KOR" is "ko"): undefined for an IRI the
+ * reference data does not describe.
+ */
+export function languageTagOf(iri: string): string | undefined {
+  const concept = EU_LANGUAGES.find((one) => one.iri === iri);
+  return concept === undefined ? undefined : TAGS[concept.code];
+}
diff --git a/packages/domain/src/library.test.ts b/packages/domain/src/library.test.ts
index 2bd39994..01a351ad 100644
--- a/packages/domain/src/library.test.ts
+++ b/packages/domain/src/library.test.ts
@@ -5,8 +5,10 @@
 import { describe, expect, it } from "vitest";
 import type { Deck } from "./deck";
 import {
+  deckCardLanguages,
   filterLibraryDecks,
   isCopyOf,
+  libraryCardLanguages,
   libraryCopiesOf,
   newestRelease,
   offersNewerRelease,
@@ -19,6 +21,8 @@ import {
 
 const TOPIC = "https://solid-memo.com/ns/vocab/topics.ttl#";
 const EDUC = "http://publications.europa.eu/resource/authority/data-theme/EDUC";
+const LANGUAGE = "http://publications.europa.eu/resource/authority/language/";
+const [ENG, SWE, KOR] = [`${LANGUAGE}ENG`, `${LANGUAGE}SWE`, `${LANGUAGE}KOR`];
 
 function libraryDeck(
   name: string,
@@ -33,6 +37,7 @@ function libraryDeck(
     releases: [],
     title: { en: name },
     cardCount: 1,
+    languages: [],
     authors: [],
     direction: "front-to-back",
     sources: [],
@@ -44,9 +49,11 @@ function libraryDeck(
 
 const capitals = libraryDeck("capitals", [`${TOPIC}geography`], {
   description: { en: "Every country's capital." },
+  languages: [ENG, SWE],
 });
 const nouns = libraryDeck("swedish-nouns", [`${TOPIC}swedish`], {
   keywords: { en: ["Vocabulary"], sv: ["Ordförråd"] },
+  languages: [SWE, ENG],
 });
 const http = libraryDeck("http", [`${TOPIC}computing`]);
 
@@ -195,46 +202,99 @@ describe("topicsOf and topicLabels", () => {
   });
 });
 
+describe("deckCardLanguages and libraryCardLanguages", () => {
+  const korean = libraryDeck("korean", [], { languages: [KOR, `${LANGUAGE}NOR`, SWE] });
+
+  it("tag a deck's card languages in its order, leaving out those the reference data does not describe", () => {
+    expect(deckCardLanguages(nouns)).toEqual([
+      { iri: SWE, tag: "sv" },
+      { iri: ENG, tag: "en" },
+    ]);
+    expect(deckCardLanguages(korean).map((language) => language.tag)).toEqual(["ko", "sv"]);
+    expect(deckCardLanguages(http)).toEqual([]);
+  });
+
+  it("list each language any deck's cards are in once, in the EU table's order", () => {
+    expect(libraryCardLanguages([korean, nouns, http]).map((language) => language.tag)).toEqual([
+      "en",
+      "sv",
+      "ko",
+    ]);
+    expect(libraryCardLanguages([http])).toEqual([]);
+  });
+});
+
 describe("filterLibraryDecks", () => {
   const decks = [capitals, nouns, http];
 
   it("keeps every deck when nothing is chosen or typed", () => {
-    expect(filterLibraryDecks(decks, { topics: [], query: "  " })).toEqual(decks);
+    expect(filterLibraryDecks(decks, { topics: [], languages: [], query: "  " })).toEqual(decks);
   });
 
   it("keeps the decks about every chosen topic, a narrower topic included", () => {
-    expect(filterLibraryDecks(decks, { topics: [`${TOPIC}languages`], query: "" })).toEqual([
+    expect(
+      filterLibraryDecks(decks, { topics: [`${TOPIC}languages`], languages: [], query: "" }),
+    ).toEqual([nouns]);
+    expect(
+      filterLibraryDecks(decks, { topics: [`${TOPIC}geography`], languages: [], query: "" }),
+    ).toEqual([capitals]);
+    expect(
+      filterLibraryDecks(decks, {
+        topics: [`${TOPIC}geography`, `${TOPIC}computing`],
+        languages: [],
+        query: "",
+      }),
+    ).toEqual([]);
+  });
+
+  it("keeps the decks with cards in every chosen language", () => {
+    const korean = libraryDeck("korean", [], { languages: [KOR, SWE] });
+    const all = [...decks, korean];
+    expect(filterLibraryDecks(all, { topics: [], languages: [SWE], query: "" })).toEqual([
+      capitals,
       nouns,
+      korean,
     ]);
-    expect(filterLibraryDecks(decks, { topics: [`${TOPIC}geography`], query: "" })).toEqual([
-      capitals,
+    expect(filterLibraryDecks(all, { topics: [], languages: [KOR, SWE], query: "" })).toEqual([
+      korean,
     ]);
+    expect(filterLibraryDecks(all, { topics: [], languages: [KOR, ENG], query: "" })).toEqual([]);
     expect(
-      filterLibraryDecks(decks, { topics: [`${TOPIC}geography`, `${TOPIC}computing`], query: "" }),
-    ).toEqual([]);
+      filterLibraryDecks(all, { topics: [`${TOPIC}swedish`], languages: [ENG], query: "" }),
+    ).toEqual([nouns]);
   });
 
   it("keeps the decks whose name, description or keywords contain the query, whatever the case", () => {
-    expect(filterLibraryDecks(decks, { topics: [], query: "HTTP" })).toEqual([http]);
-    expect(filterLibraryDecks(decks, { topics: [], query: "capital" })).toEqual([capitals]);
-    expect(filterLibraryDecks(decks, { topics: [], query: "vocabulary" })).toEqual([nouns]);
+    expect(filterLibraryDecks(decks, { topics: [], languages: [], query: "HTTP" })).toEqual([http]);
+    expect(filterLibraryDecks(decks, { topics: [], languages: [], query: "capital" })).toEqual([
+      capitals,
+    ]);
+    expect(filterLibraryDecks(decks, { topics: [], languages: [], query: "vocabulary" })).toEqual([
+      nouns,
+    ]);
   });
 
   it("searches the keywords in every language, not only the reader's", () => {
-    expect(filterLibraryDecks(decks, { topics: [], query: "ordförråd" })).toEqual([nouns]);
+    expect(filterLibraryDecks(decks, { topics: [], languages: [], query: "ordförråd" })).toEqual([
+      nouns,
+    ]);
   });
 
   it("finds composed text with a decomposed query, and decomposed text with a composed one", () => {
     const korean = libraryDeck("korean-nouns", [`${TOPIC}korean`], { keywords: { ko: ["사람"] } });
     const decomposed = libraryDeck("decomposed", [], { description: { en: "Cafe\u0301 words" } });
     expect(
-      filterLibraryDecks([...decks, korean], { topics: [], query: "사람".normalize("NFD") }),
+      filterLibraryDecks([...decks, korean], {
+        topics: [],
+        languages: [],
+        query: "사람".normalize("NFD"),
+      }),
     ).toEqual([korean]);
-    expect(filterLibraryDecks([...decks, decomposed], { topics: [], query: "CAFÉ" })).toEqual([
-      decomposed,
-    ]);
-    expect(filterLibraryDecks(decks, { topics: [], query: "ordfo\u0308rra\u030Ad" })).toEqual([
-      nouns,
-    ]);
+    expect(
+      filterLibraryDecks([...decks, decomposed], { topics: [], languages: [], query: "CAFÉ" }),
+    ).toEqual([decomposed]);
+    expect(
+      filterLibraryDecks(decks, { topics: [], languages: [], query: "ordfo\u0308rra\u030Ad" }),
+    ).toEqual([nouns]);
   });
 });
diff --git a/packages/domain/src/library.ts b/packages/domain/src/library.ts
index 940a6b29..c6dc377f 100644
--- a/packages/domain/src/library.ts
+++ b/packages/domain/src/library.ts
@@ -2,8 +2,9 @@
 //
 // SPDX-License-Identifier: MIT
 
-import { TOPICS } from "@solid-memo/vocab/concepts.generated";
+import { EU_LANGUAGES, TOPICS } from "@solid-memo/vocab/concepts.generated";
 import type { CardContent, Deck, DeckDirection } from "./deck";
+import { languageTagOf } from "./euLanguages";
 import { allKeywords, type LangTexts } from "./keywords";
 import type { LangText } from "./langText";
 import { librarySeriesUrlOf } from "./libraryLayout";
@@ -33,6 +34,12 @@ export interface LibraryDeck {
   /** The deck's title, in every language it states it in (one of them English). */
   title: LangText;
   cardCount: number;
+  /**
+   * The languages the current release's cards are in (dcterms:language),
+   * by their IRIs in the EU's table, in the order the release gives them:
+   * none when it states none, as a release published elsewhere may.
+   */
+  languages: string[];
   authors: string[];
   license?: string;
   /** A sentence or two about the deck, in every language it states it in. */
@@ -225,19 +232,46 @@ function isAbout(deck: LibraryDeck, topic: string): boolean {
   );
 }
 
+/** A language a library deck's cards are in: its IRI in the EU's table and its language tag. */
+export interface CardLanguage {
+  iri: string;
+  tag: string;
+}
+
+/** The languages a deck's cards are in, in its order: those the reference data describes (languageTagOf), any other left out. */
+export function deckCardLanguages(deck: Pick<LibraryDeck, "languages">): CardLanguage[] {
+  return deck.languages.flatMap((iri) => {
+    const tag = languageTagOf(iri);
+    return tag === undefined ? [] : [{ iri, tag }];
+  });
+}
+
+/** The languages the decks' cards are in, to filter the library by: each any deck states, in the EU table's order. */
+export function libraryCardLanguages(decks: readonly LibraryDeck[]): CardLanguage[] {
+  const stated = new Set(decks.flatMap((deck) => deck.languages));
+  return deckCardLanguages({
+    languages: EU_LANGUAGES.map((concept) => concept.iri).filter((iri) => stated.has(iri)),
+  });
+}
+
 /**
- * The decks about every chosen topic whose title, description or
- * keywords, in any language, contain the query (case-insensitively,
- * whatever its Unicode form: see search.ts); all of them when nothing is
- * chosen or typed.
+ * The decks about every chosen topic, with cards in every chosen
+ * language, whose title, description or keywords, in any language,
+ * contain the query (case-insensitively, whatever its Unicode form: see
+ * search.ts); all of them when nothing is chosen or typed.
  */
 export function filterLibraryDecks(
   decks: readonly LibraryDeck[],
-  { topics, query }: { topics: readonly string[]; query: string },
+  {
+    topics,
+    languages,
+    query,
+  }: { topics: readonly string[]; languages: readonly string[]; query: string },
 ): LibraryDeck[] {
   return decks.filter(
     (deck) =>
       topics.every((topic) => isAbout(deck, topic)) &&
+      languages.every((language) => deck.languages.includes(language)) &&
       matchesQuery(
         [
           ...Object.values(deck.title),
diff --git a/packages/domain/src/release/draftListing.test.ts b/packages/domain/src/release/draftListing.test.ts
index 83fe7ba1..586457a8 100644
--- a/packages/domain/src/release/draftListing.test.ts
+++ b/packages/domain/src/release/draftListing.test.ts
@@ -27,6 +27,7 @@ describe("draftLibraryDeck", () => {
       keywords: {},
       title: { en: "Solid" },
       cardCount: 3,
+      languages: [],
       authors: [],
       direction: "front-to-back",
       createdAt: NOW,
@@ -51,6 +52,7 @@ describe("draftLibraryDeck", () => {
         creator: [of("anna"), "https://someone.example/#me"],
         theme: ["https://theme.example/"],
         keyword: { en: ["word"] },
+        language: ["http://publications.europa.eu/resource/authority/language/SWE"],
         wasDerivedFrom: ["https://source.example/"],
       },
       agents: [{ id: "anna", data: { name: "Anna" } }],
@@ -85,6 +87,7 @@ describe("draftLibraryDeck", () => {
       releases: [{ url: DRAFT, version: "1", issued: NOW, notes: "First" }],
       themes: ["https://theme.example/"],
       keywords: { en: ["word"] },
+      languages: ["http://publications.europa.eu/resource/authority/language/SWE"],
       authors: ["Anna", "https://someone.example/#me"],
       license: "https://creativecommons.org/publicdomain/zero/1.0/",
       description: { en: "About" },
diff --git a/packages/domain/src/release/draftListing.ts b/packages/domain/src/release/draftListing.ts
index 098c16b2..ed2a4c4a 100644
--- a/packages/domain/src/release/draftListing.ts
+++ b/packages/domain/src/release/draftListing.ts
@@ -43,6 +43,7 @@ export function draftLibraryDeck(draft: ReleaseDraft): LibraryDeck {
     keywords: copyKeywords(root.keyword),
     title: root.title ?? {},
     cardCount: draft.cards.filter((card) => card.data.deprecated !== true).length,
+    languages: [...root.language],
     authors: root.creator.map((agent) => names.get(agent) ?? agent),
     ...(root.license === undefined ? {} : { license: root.license }),
     ...(root.description === undefined ? {} : { description: root.description }),
@@ -78,6 +79,7 @@ export function draftLibraryContent(draft: ReleaseDraft): LibraryDeckContent {
     url,
     releases: _releases,
     cardCount: _cardCount,
+    languages: _languages,
     sources: _sources,
     createdAt: _createdAt,
     isCourse,
diff --git a/packages/solid/src/mappers/libraryMapper.test.ts b/packages/solid/src/mappers/libraryMapper.test.ts
index 60fe1e76..02d1c43b 100644
--- a/packages/solid/src/mappers/libraryMapper.test.ts
+++ b/packages/solid/src/mappers/libraryMapper.test.ts
@@ -30,6 +30,7 @@ const CC0 = "https://creativecommons.org/publicdomain/zero/1.0/";
 const SERIES = "https://solid-memo.com/decks/index.ttl#capitals";
 const EDUC = "http://publications.europa.eu/resource/authority/data-theme/EDUC";
 const FLAG = "https://flagcdn.com/af.svg";
+const LANGUAGE = "http://publications.europa.eu/resource/authority/language/";
 
 function thing(
   url: string,
@@ -71,6 +72,7 @@ const INDEX_TURTLE = `
    dcterms:issued "2026-09-22T10:00:00Z"^^xsd:dateTime ;
    dcterms:publisher <#solid-memo> ; sm:studyDirection sm:bidirectional ;
    dcat:theme <${EDUC}>, <https://solid-memo.com/ns/vocab/topics.ttl#geography> ; dcat:keyword "capitals" ;
+   dcterms:language <${LANGUAGE}SWE>, <${LANGUAGE}ENG> ;
    dcat:version "2" ; adms:versionNotes "Added Norway." ;
    dcat:inSeries <#capitals> ; dcat:isVersionOf <#capitals> ; dcat:distribution <capitals/v2.ttl#turtle> ;
    prov:wasDerivedFrom <${WIKIPEDIA}>, <https://iupac.org/>, <${WIKIDATA}> .
@@ -113,6 +115,7 @@ describe("toLibraryDecks", () => {
         ],
         title: { en: "Capitals" },
         cardCount: 243,
+        languages: [`${LANGUAGE}SWE`, `${LANGUAGE}ENG`],
         authors: ["Anton <anton@example.com>", "https://solid-memo.com/decks/capitals/v2.ttl#gone"],
         license: CC0,
         description: { en: "Capitals of the world." },
diff --git a/packages/solid/src/mappers/libraryMapper.ts b/packages/solid/src/mappers/libraryMapper.ts
index cbaedd3b..498a5b4c 100644
--- a/packages/solid/src/mappers/libraryMapper.ts
+++ b/packages/solid/src/mappers/libraryMapper.ts
@@ -104,6 +104,7 @@ function toLibraryDeck(
       .sort((a, b) => Number(a.version) - Number(b.version)),
     title: release.title,
     cardCount: getInteger(currentThing!, SM.cardCount) ?? 0,
+    languages: [...release.language],
     authors: release.creator.map((agent) => names.get(agent) ?? agent),
     ...(release.license === undefined ? {} : { license: release.license }),
     description: release.description,
@@ -238,6 +239,7 @@ export function toStandaloneLibraryDeck(url: string, dataset: SolidDataset): Lib
       .map((one) => (one.url === subject ? { ...one, url } : one))
       .sort((a, b) => Number(a.version) - Number(b.version)),
     cardCount: cards.filter((card) => card.retired !== true).length,
+    languages: [...release.language],
     ...(release.created === undefined ? {} : { createdAt: release.created }),
     sources: release.wasDerivedFrom.map((sourceUrl) =>
       toLibrarySource(sourceUrl, getThing(dataset, sourceUrl)),
diff --git a/packages/solid/src/releaseFromLink.test.ts b/packages/solid/src/releaseFromLink.test.ts
index cb0a8678..58845204 100644
--- a/packages/solid/src/releaseFromLink.test.ts
+++ b/packages/solid/src/releaseFromLink.test.ts
@@ -64,6 +64,10 @@ describe("readRelease", () => {
       title: { en: "Capitals", sv: "Huvudstäder" },
       description: { en: "Capitals of the world.", sv: "Världens huvudstäder." },
       cardCount: 2,
+      languages: [
+        "http://publications.europa.eu/resource/authority/language/ENG",
+        "http://publications.europa.eu/resource/authority/language/SWE",
+      ],
       authors: ["Alice"],
       license: "https://creativecommons.org/publicdomain/zero/1.0/",
       direction: "front-to-back",
diff --git a/packages/ui/src/i18n/de.json b/packages/ui/src/i18n/de.json
index 18ef4dfa..85492f1c 100644
--- a/packages/ui/src/i18n/de.json
+++ b/packages/ui/src/i18n/de.json
@@ -831,6 +831,7 @@
     "intro": "Fertige Kartenstapel. Öffne einen, um mehr darüber zu lesen, oder kreuze mehrere an und importiere sie als eigene Kopien in diese Instanz.",
     "empty": "Die Bibliothek hat noch keine Stapel.",
     "topics": "Themen",
+    "cardLanguages": "Sprachen der Karten",
     "search": "Suche",
     "searchPlaceholder": "Name, Beschreibung oder Schlagwort",
     "noMatch": "Kein Stapel passt.",
@@ -874,6 +875,10 @@
       "one": "Thema",
       "other": "Themen"
     },
+    "cardLanguages": {
+      "one": "Sprache der Karten",
+      "other": "Sprachen der Karten"
+    },
     "keywords": "Schlagwörter",
     "release": "Ausgabe",
     "version": "Version {version}",
@@ -911,6 +916,7 @@
     "back": "Zurück zur Bibliothek",
     "empty": "Dieser Stapel hat keine Karten.",
     "hint": "Zufällige Karten aus dem Stapel. Nichts wird gespeichert: Importiere den Stapel, um ihn zu lernen.",
+    "cardLanguages": "Karten auf {languages}.",
     "nextCard": "Nächste Karte",
     "reveal": "Antwort anzeigen",
     "loading": "Karten werden geladen…"
diff --git a/packages/ui/src/i18n/en.json b/packages/ui/src/i18n/en.json
index 99da0f79..ef00c9c2 100644
--- a/packages/ui/src/i18n/en.json
+++ b/packages/ui/src/i18n/en.json
@@ -831,6 +831,7 @@
     "intro": "Ready-made decks. Open one to read about it, or check several and import them into this instance as your own copies.",
     "empty": "The library has no decks yet.",
     "topics": "Topics",
+    "cardLanguages": "Card languages",
     "search": "Search",
     "searchPlaceholder": "Name, description or keyword",
     "noMatch": "No deck matches.",
@@ -874,6 +875,10 @@
       "one": "Topic",
       "other": "Topics"
     },
+    "cardLanguages": {
+      "one": "Card language",
+      "other": "Card languages"
+    },
     "keywords": "Keywords",
     "release": "Release",
     "version": "Version {version}",
@@ -911,6 +916,7 @@
     "back": "Back to library",
     "empty": "This deck has no cards.",
     "hint": "Random cards from the deck. Nothing is recorded: import the deck to study it.",
+    "cardLanguages": "Cards in {languages}.",
     "nextCard": "Next card",
     "reveal": "Reveal",
     "loading": "Loading cards…"
diff --git a/packages/ui/src/i18n/es.json b/packages/ui/src/i18n/es.json
index 0a363375..73c5f2a8 100644
--- a/packages/ui/src/i18n/es.json
+++ b/packages/ui/src/i18n/es.json
@@ -873,6 +873,7 @@
     "intro": "Mazos ya preparados. Abre uno para ver de qué trata, o marca varios e impórtalos a esta instancia como copias tuyas.",
     "empty": "La biblioteca aún no tiene mazos.",
     "topics": "Temas",
+    "cardLanguages": "Idiomas de las tarjetas",
     "search": "Buscar",
     "searchPlaceholder": "Nombre, descripción o palabra clave",
     "noMatch": "Ningún mazo coincide.",
@@ -919,6 +920,11 @@
       "many": "Temas",
       "other": "Temas"
     },
+    "cardLanguages": {
+      "one": "Idioma de las tarjetas",
+      "many": "Idiomas de las tarjetas",
+      "other": "Idiomas de las tarjetas"
+    },
     "keywords": "Palabras clave",
     "release": "Publicación",
     "version": "Versión {version}",
@@ -958,6 +964,7 @@
     "back": "Volver a la biblioteca",
     "empty": "Este mazo no tiene tarjetas.",
     "hint": "Tarjetas al azar del mazo. No se registra nada: importa el mazo para estudiarlo.",
+    "cardLanguages": "Tarjetas en {languages}.",
     "nextCard": "Siguiente tarjeta",
     "reveal": "Mostrar respuesta",
     "loading": "Cargando tarjetas…"
diff --git a/packages/ui/src/i18n/fr.json b/packages/ui/src/i18n/fr.json
index a9a3b40d..d2619a9c 100644
--- a/packages/ui/src/i18n/fr.json
+++ b/packages/ui/src/i18n/fr.json
@@ -873,6 +873,7 @@
     "intro": "Des paquets prêts à l’emploi. Ouvrez-en un pour en savoir plus, ou cochez-en plusieurs et importez-les dans cette instance comme vos propres copies.",
     "empty": "La bibliothèque n’a pas encore de paquets.",
     "topics": "Thèmes",
+    "cardLanguages": "Langues des cartes",
     "search": "Rechercher",
     "searchPlaceholder": "Nom, description ou mot-clé",
     "noMatch": "Aucun paquet ne correspond.",
@@ -919,6 +920,11 @@
       "many": "Thèmes",
       "other": "Thèmes"
     },
+    "cardLanguages": {
+      "one": "Langue des cartes",
+      "many": "Langues des cartes",
+      "other": "Langues des cartes"
+    },
     "keywords": "Mots-clés",
     "release": "Version",
     "version": "Version {version}",
@@ -958,6 +964,7 @@
     "back": "Retour à la bibliothèque",
     "empty": "Ce paquet ne contient aucune carte.",
     "hint": "Des cartes du paquet tirées au hasard. Rien n’est enregistré : importez le paquet pour l’étudier.",
+    "cardLanguages": "Cartes en {languages}.",
     "nextCard": "Carte suivante",
     "reveal": "Afficher la réponse",
     "loading": "Chargement des cartes…"
diff --git a/packages/ui/src/i18n/ko.json b/packages/ui/src/i18n/ko.json
index c28eb2f2..75404264 100644
--- a/packages/ui/src/i18n/ko.json
+++ b/packages/ui/src/i18n/ko.json
@@ -789,6 +789,7 @@
     "intro": "바로 쓸 수 있는 덱이에요. 덱을 열어 자세히 보거나, 여러 개를 선택해 이 인스턴스에 내 복사본으로 가져올 수 있어요.",
     "empty": "라이브러리에 아직 덱이 없어요.",
     "topics": "주제",
+    "cardLanguages": "카드 언어",
     "search": "검색",
     "searchPlaceholder": "이름, 설명 또는 키워드",
     "noMatch": "일치하는 덱이 없어요.",
@@ -829,6 +830,9 @@
     "topics": {
       "other": "주제"
     },
+    "cardLanguages": {
+      "other": "카드 언어"
+    },
     "keywords": "키워드",
     "release": "릴리스",
     "version": "버전 {version}",
@@ -864,6 +868,7 @@
     "back": "덱 라이브러리로 돌아가기",
     "empty": "이 덱에는 카드가 없어요.",
     "hint": "덱에서 무작위로 고른 카드예요. 아무것도 기록되지 않아요. 학습하려면 덱을 가져와 주세요.",
+    "cardLanguages": "카드 언어: {languages}",
     "nextCard": "다음 카드",
     "reveal": "정답 보기",
     "loading": "카드를 불러오는 중…"
diff --git a/packages/ui/src/i18n/sv.json b/packages/ui/src/i18n/sv.json
index c0e1dcd3..02461bf6 100644
--- a/packages/ui/src/i18n/sv.json
+++ b/packages/ui/src/i18n/sv.json
@@ -831,6 +831,7 @@
     "intro": "Färdiga kortlekar. Öppna en för att läsa om den, eller kryssa i flera och importera dem till den här instansen som egna kopior.",
     "empty": "Biblioteket har inga kortlekar än.",
     "topics": "Ämnen",
+    "cardLanguages": "Kortens språk",
     "search": "Sök",
     "searchPlaceholder": "Namn, beskrivning eller nyckelord",
     "noMatch": "Ingen kortlek matchar.",
@@ -874,6 +875,10 @@
       "one": "Ämne",
       "other": "Ämnen"
     },
+    "cardLanguages": {
+      "one": "Kortens språk",
+      "other": "Kortens språk"
+    },
     "keywords": "Nyckelord",
     "release": "Utgåva",
     "version": "Version {version}",
@@ -911,6 +916,7 @@
     "back": "Tillbaka till biblioteket",
     "empty": "Kortleken har inga kort.",
     "hint": "Slumpade kort ur kortleken. Inget sparas: importera kortleken för att studera den.",
+    "cardLanguages": "Korten är på {languages}.",
     "nextCard": "Nästa kort",
     "reveal": "Visa svar",
     "loading": "Läser in kort…"
diff --git a/packages/ui/src/style.css b/packages/ui/src/style.css
index 2f0ed3cd..95b3f7f4 100644
--- a/packages/ui/src/style.css
+++ b/packages/ui/src/style.css
@@ -2037,17 +2037,20 @@ html.drag-active {
   margin-top: 0.35rem;
 }
 
-.library-topics {
+.library-topics,
+.library-languages {
   display: flex;
   flex-wrap: wrap;
   gap: 0.25rem 1rem;
 }
 
-.library-topics legend {
+.library-topics legend,
+.library-languages legend {
   width: 100%;
 }
 
-.library-topics label.checkbox-option {
+.library-topics label.checkbox-option,
+.library-languages label.checkbox-option {
   display: inline-flex;
   align-items: center;
   gap: 0.35rem;
@@ -2124,8 +2127,8 @@ html.drag-active {
 }
 
 /* As in the deck list: the checkbox beside the name, which wraps,
-   and the size under the name, followed by the imported badge,
-   which wraps below it when there is no room. */
+   and the size under the name, followed by the card languages and the
+   imported badge, which wrap below it when there is no room. */
 .library-deck-meta {
   grid-column: 2;
   grid-row: 2;
@@ -2149,6 +2152,13 @@ html.drag-active {
   font-variant-numeric: tabular-nums;
 }
 
+/* A deck's card languages may be many: they shrink and wrap, a name at a time. */
+.library-list .library-card-languages {
+  flex-shrink: 1;
+  min-width: 0;
+  white-space: normal;
+}
+
 .provenance {
   display: block;
   margin: -0.25rem 0 0.75rem;
diff --git a/packages/ui/src/test/course.ts b/packages/ui/src/test/course.ts
index 4b7fdbb5..0c9972d3 100644
--- a/packages/ui/src/test/course.ts
+++ b/packages/ui/src/test/course.ts
@@ -27,6 +27,7 @@ export const courseLibraryDeck: LibraryDeck = {
   ...firstRelease(RELEASE),
   title: { en: "Solid fundamentals", sv: "Solids grunder" },
   cardCount: 5,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
diff --git a/packages/ui/src/ui/ImportUrlContainer.test.tsx b/packages/ui/src/ui/ImportUrlContainer.test.tsx
index 4c8be9ec..80636a6d 100644
--- a/packages/ui/src/ui/ImportUrlContainer.test.tsx
+++ b/packages/ui/src/ui/ImportUrlContainer.test.tsx
@@ -25,6 +25,7 @@ const rivers: LibraryDeck = {
   title: { en: "Rivers" },
   description: { en: "The longest rivers." },
   cardCount: 3,
+  languages: [],
   authors: ["Bob"],
   license: "https://creativecommons.org/publicdomain/zero/1.0/",
   direction: "front-to-back",
diff --git a/packages/ui/src/ui/LibraryBrowserContainer.test.tsx b/packages/ui/src/ui/LibraryBrowserContainer.test.tsx
index ecd52cb2..23e2a66e 100644
--- a/packages/ui/src/ui/LibraryBrowserContainer.test.tsx
+++ b/packages/ui/src/ui/LibraryBrowserContainer.test.tsx
@@ -16,6 +16,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals" },
   cardCount: 1,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
diff --git a/packages/ui/src/ui/LibraryBrowserScreen.test.tsx b/packages/ui/src/ui/LibraryBrowserScreen.test.tsx
index d8266c5e..6dd8ea59 100644
--- a/packages/ui/src/ui/LibraryBrowserScreen.test.tsx
+++ b/packages/ui/src/ui/LibraryBrowserScreen.test.tsx
@@ -14,6 +14,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals" },
   cardCount: 2,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
diff --git a/packages/ui/src/ui/LibraryContainer.test.tsx b/packages/ui/src/ui/LibraryContainer.test.tsx
index 81c1808b..98c2b196 100644
--- a/packages/ui/src/ui/LibraryContainer.test.tsx
+++ b/packages/ui/src/ui/LibraryContainer.test.tsx
@@ -24,6 +24,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals" },
   cardCount: 2,
+  languages: [],
   authors: ["Anton Wiklund"],
   license: "https://creativecommons.org/publicdomain/zero/1.0/",
   direction: "front-to-back",
@@ -34,6 +35,7 @@ const rivers: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/rivers/v1.ttl"),
   title: { en: "Rivers" },
   cardCount: 1,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
@@ -68,7 +70,8 @@ function renderContainer(useCases: UseCases) {
 describe("LibraryContainer", () => {
   // The library remembers its checked decks and filters per instance; each test starts afresh.
   afterEach(() => {
-    for (const part of ["selected", "topics", "query"]) forget(`library:${instance.url}:${part}`);
+    for (const part of ["selected", "topics", "languages", "query"])
+      forget(`library:${instance.url}:${part}`);
   });
 
   it("shows a loading state, then the library", async () => {
diff --git a/packages/ui/src/ui/LibraryDeckContainer.test.tsx b/packages/ui/src/ui/LibraryDeckContainer.test.tsx
index 917aeff8..ec195f2e 100644
--- a/packages/ui/src/ui/LibraryDeckContainer.test.tsx
+++ b/packages/ui/src/ui/LibraryDeckContainer.test.tsx
@@ -23,6 +23,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals" },
   cardCount: 2,
+  languages: [],
   authors: ["Anton Wiklund"],
   direction: "front-to-back",
   sources: [],
diff --git a/packages/ui/src/ui/LibraryDeckScreen.test.tsx b/packages/ui/src/ui/LibraryDeckScreen.test.tsx
index e864d367..d8fd5d2c 100644
--- a/packages/ui/src/ui/LibraryDeckScreen.test.tsx
+++ b/packages/ui/src/ui/LibraryDeckScreen.test.tsx
@@ -22,6 +22,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals of the world" },
   cardCount: 243,
+  languages: [],
   authors: ["Anton Wiklund"],
   license: CC0,
   description: { en: `Every country and its capital. Compiled from ${WIKIPEDIA}.` },
@@ -123,6 +124,17 @@ describe("LibraryDeckScreen", () => {
     expect(screen.queryByText("Keywords", { selector: "dt" })).toBeNull();
   });
 
+  it("names the languages its cards are in, in the deck's order, the singular for one", () => {
+    const LANGUAGE = "http://publications.europa.eu/resource/authority/language/";
+    const { unmount } = renderScreen({
+      deck: { ...capitals, languages: [`${LANGUAGE}SWE`, `${LANGUAGE}ENG`] },
+    });
+    expect(fact("Card languages")).toHaveTextContent(/^Swedish, English$/);
+    unmount();
+    renderScreen({ deck: { ...capitals, languages: [`${LANGUAGE}KOR`] } });
+    expect(fact("Card language")).toHaveTextContent(/^Korean$/);
+  });
+
   it("uses the singular for one topic", () => {
     renderScreen({
       deck: { ...capitals, themes: ["https://solid-memo.com/ns/vocab/topics.ttl#geography"] },
@@ -222,6 +234,7 @@ describe("LibraryDeckScreen", () => {
         ...firstRelease(capitals.url),
         title: { en: "Rivers" },
         cardCount: 1,
+        languages: [],
         authors: [],
         direction: "front-to-back",
         sources: [],
diff --git a/packages/ui/src/ui/LibraryDeckScreen.tsx b/packages/ui/src/ui/LibraryDeckScreen.tsx
index cd9a6336..e8e70791 100644
--- a/packages/ui/src/ui/LibraryDeckScreen.tsx
+++ b/packages/ui/src/ui/LibraryDeckScreen.tsx
@@ -8,6 +8,7 @@ import { keywordsIn } from "@solid-memo/domain/keywords";
 import { topicLabels, type LibraryDeck, type LibrarySource } from "@solid-memo/domain/library";
 import type { ReportPlace } from "@solid-memo/domain/mistakeReport";
 import { AuthorNames } from "./AuthorName";
+import { cardLanguageNames } from "./cardLanguageNames";
 import { ErrorMessage } from "./ErrorMessage";
 import { ExternalLink } from "./ExternalLink";
 import { useI18n, type ErrorText } from "./i18n";
@@ -17,8 +18,8 @@ import { ReaderText, ReaderTexts } from "./ReaderText";
 import { ReportMistake } from "./ReportMistake";
 
 /**
- * One library deck in full — its blurb, what it is about (its keywords
- * only those in the reader's language), who made it
+ * One library deck in full — its blurb, the languages its cards are in,
+ * what it is about (its keywords only those in the reader's language), who made it
  * and under what terms, when it was made and last changed, which
  * release it is and what changed in it, and what it was compiled from —
  * with a look at its cards and an import button for this deck alone.
@@ -68,8 +69,10 @@ export function LibraryDeckScreen({
   /** Where a mistake in the release is reported (UseCases.reportPlace); none while it is read. */
   reportPlace?: ReportPlace;
 }) {
-  const { t, locale, readerText, readerLang, formatDate, directionLabel } = useI18n();
+  const { t, locale, readerText, readerLang, formatDate, directionLabel, languageParts } =
+    useI18n();
   const topics = topicLabels(deck.themes);
+  const languages = cardLanguageNames(deck, languageParts);
   /** Only those in the reader's language: none in it, no keywords shown. */
   const keywords = keywordsIn(deck.keywords, locale);
   const current = deck.releases.find((release) => release.url === deck.url);
@@ -105,6 +108,12 @@ export function LibraryDeckScreen({
         )}
         <dt>{t("libraryDeck.size")}</dt>
         <dd>{t("common.cardCount", { count: deck.cardCount })}</dd>
+        {languages.length > 0 && (
+          <>
+            <dt>{t("libraryDeck.cardLanguages", { count: languages.length })}</dt>
+            <dd>{languages.join(", ")}</dd>
+          </>
+        )}
         <dt>{t("libraryDeck.studied")}</dt>
         <dd>
           {deck.direction === "bidirectional"
diff --git a/packages/ui/src/ui/LibraryPreviewContainer.test.tsx b/packages/ui/src/ui/LibraryPreviewContainer.test.tsx
index af9a313f..92ff64b6 100644
--- a/packages/ui/src/ui/LibraryPreviewContainer.test.tsx
+++ b/packages/ui/src/ui/LibraryPreviewContainer.test.tsx
@@ -16,6 +16,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals" },
   cardCount: 3,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
@@ -82,6 +83,25 @@ describe("LibraryPreviewContainer", () => {
     expect(listLibraryCards).toHaveBeenCalledWith(capitals);
   });
 
+  it("names the languages the deck says its cards are in", async () => {
+    renderContainer({
+      deck: {
+        ...capitals,
+        languages: [
+          "http://publications.europa.eu/resource/authority/language/ENG",
+          "http://publications.europa.eu/resource/authority/language/SWE",
+        ],
+      },
+    });
+    expect(await screen.findByText("Cards in English, Swedish.")).toBeInTheDocument();
+  });
+
+  it("names no card languages for a deck that states none", async () => {
+    renderContainer();
+    await screen.findByRole("heading", { name: "Preview: Capitals" });
+    expect(screen.queryByText(/^Cards in/)).toBeNull();
+  });
+
   it("shows the question's note only once the answer is revealed", async () => {
     const noted = [{ ...card("Sweden", "Stockholm"), frontNote: { en: "A kingdom." } }];
     renderContainer({ useCases: makeUseCasesFake({ listLibraryCards: vi.fn(async () => noted) }) });
diff --git a/packages/ui/src/ui/LibraryPreviewContainer.tsx b/packages/ui/src/ui/LibraryPreviewContainer.tsx
index 2f6e6458..c35e3486 100644
--- a/packages/ui/src/ui/LibraryPreviewContainer.tsx
+++ b/packages/ui/src/ui/LibraryPreviewContainer.tsx
@@ -7,6 +7,7 @@ import { useQuery } from "@tanstack/react-query";
 import type { UseCases } from "@solid-memo/application/useCases";
 import { activeCards, studyDirections } from "@solid-memo/domain/deck";
 import type { LibraryDeck } from "@solid-memo/domain/library";
+import { cardLanguageNames } from "./cardLanguageNames";
 import { ErrorMessage } from "./ErrorMessage";
 import { useI18n } from "./i18n";
 import { LibraryPreviewScreen, type PreviewPrompt } from "./LibraryPreviewScreen";
@@ -32,7 +33,7 @@ export function LibraryPreviewContainer({
   /** Uniform [0, 1) source picking the next card. */
   random?: () => number;
 }) {
-  const { t, readerText, readerLang, errorText } = useI18n();
+  const { t, readerText, readerLang, errorText, languageParts } = useI18n();
   const cardsQuery = useQuery({
     queryKey: queryKeys.libraryCards(deck.url),
     queryFn: () => useCases.listLibraryCards(deck),
@@ -65,6 +66,7 @@ export function LibraryPreviewContainer({
       deckName={readerText(deck.title)}
       deckLang={readerLang(deck.title)}
       deckHref={deckHref}
+      cardLanguages={cardLanguageNames(deck, languageParts)}
       prompt={prompts.length === 0 ? null : prompts[index]}
       turn={turn}
       onNext={next}
diff --git a/packages/ui/src/ui/LibraryPreviewScreen.tsx b/packages/ui/src/ui/LibraryPreviewScreen.tsx
index 6af32d42..e3b23e35 100644
--- a/packages/ui/src/ui/LibraryPreviewScreen.tsx
+++ b/packages/ui/src/ui/LibraryPreviewScreen.tsx
@@ -16,12 +16,14 @@ export interface PreviewPrompt {
 /**
  * A try of a library deck before importing it: its cards one at a time,
  * as study shows them, but with nothing graded or recorded — after the
- * answer comes the next card, for as long as the user likes.
+ * answer comes the next card, for as long as the user likes. The
+ * languages the deck says its cards are in are named above them.
  */
 export function LibraryPreviewScreen({
   deckName,
   deckLang,
   deckHref,
+  cardLanguages,
   prompt,
   turn,
   onNext,
@@ -32,6 +34,8 @@ export function LibraryPreviewScreen({
   deckLang?: string;
   /** URL of the deck's page; its name links there. */
   deckHref: string;
+  /** The languages the deck's cards are in, named in the app's language; none when it states none. */
+  cardLanguages: string[];
   /** null when the deck has no cards. */
   prompt: PreviewPrompt | null;
   /** Counts the cards shown, so each one starts unrevealed, even a repeat. */
@@ -59,6 +63,11 @@ export function LibraryPreviewScreen({
       ) : (
         <>
           <p class="hint">{t("libraryPreview.hint")}</p>
+          {cardLanguages.length > 0 && (
+            <p class="hint">
+              {t("libraryPreview.cardLanguages", { languages: cardLanguages.join(", ") })}
+            </p>
+          )}
           <PreviewCard key={turn} prompt={prompt} onNext={onNext} />
         </>
       )}
diff --git a/packages/ui/src/ui/LibraryScreen.test.tsx b/packages/ui/src/ui/LibraryScreen.test.tsx
index b64873cb..d269b3f7 100644
--- a/packages/ui/src/ui/LibraryScreen.test.tsx
+++ b/packages/ui/src/ui/LibraryScreen.test.tsx
@@ -16,6 +16,7 @@ const capitals: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/capitals/v1.ttl"),
   title: { en: "Capitals of the world" },
   cardCount: 243,
+  languages: [],
   authors: ["Anton Wiklund"],
   license: "https://creativecommons.org/publicdomain/zero/1.0/",
   description: { en: "Every country and its capital, from Wikipedia." },
@@ -27,6 +28,7 @@ const rivers: LibraryDeck = {
   ...firstRelease("https://solid-memo.com/decks/rivers/v1.ttl"),
   title: { en: "Rivers" },
   cardCount: 1,
+  languages: [],
   authors: [],
   direction: "front-to-back",
   sources: [],
@@ -151,6 +153,59 @@ describe("LibraryScreen", () => {
     expect(screen.queryByRole("group", { name: "Topics" })).toBeNull();
   });
 
+  describe("card languages", () => {
+    const LANGUAGE = "http://publications.europa.eu/resource/authority/language/";
+    const english = { ...capitals, languages: [`${LANGUAGE}ENG`, `${LANGUAGE}SWE`] };
+    const korean = {
+      ...rivers,
+      title: { en: "Korean nouns" },
+      languages: [`${LANGUAGE}KOR`, `${LANGUAGE}SWE`, "https://example.org/unknown"],
+    };
+
+    it("names the languages of each deck's cards beside its size, in the deck's order", () => {
+      renderScreen({ decks: [english, korean, { ...rivers, url: "none" }] });
+      expect(screen.getByText("English, Swedish")).toBeInTheDocument();
+      expect(screen.getByText("Korean, Swedish")).toBeInTheDocument();
+    });
+
+    it("offers the languages the decks state, by name, in the language the user reads", () => {
+      renderScreen({ decks: [english, korean] }, "sv");
+      const group = screen.getByRole("group", { name: "Kortens språk" });
+      expect([...group.querySelectorAll("label")].map((l) => l.textContent)).toEqual([
+        "engelska",
+        "koreanska",
+        "svenska",
+      ]);
+    });
+
+    it("narrows the list to the decks with cards in every checked language", () => {
+      renderScreen({ decks: [english, korean] });
+      fireEvent.click(screen.getByRole("checkbox", { name: "Swedish" }));
+      expect(screen.getByText("2 decks")).toBeInTheDocument();
+      fireEvent.click(screen.getByRole("checkbox", { name: "Korean" }));
+      expect(screen.queryByRole("checkbox", { name: "Capitals of the world" })).toBeNull();
+      expect(screen.getByRole("checkbox", { name: "Korean nouns" })).toBeInTheDocument();
+      expect(screen.getByText("1 of 2 decks")).toBeInTheDocument();
+      fireEvent.click(screen.getByRole("checkbox", { name: "English" }));
+      expect(screen.getByText("No deck matches.")).toBeInTheDocument();
+    });
+
+    it("remembers the checked languages between visits", () => {
+      const memoryKey = `library-test-languages-${++renders}`;
+      const { unmount } = renderScreen({ decks: [english, korean], memoryKey });
+      fireEvent.click(screen.getByRole("checkbox", { name: "Korean" }));
+      unmount();
+      renderScreen({ decks: [english, korean], memoryKey });
+      expect(screen.getByRole("checkbox", { name: "Korean" })).toBeChecked();
+      expect(screen.queryByRole("checkbox", { name: "Capitals of the world" })).toBeNull();
+    });
+
+    it("offers no languages when no deck states one", () => {
+      renderScreen();
+      expect(screen.queryByRole("group", { name: "Card languages" })).toBeNull();
+    });
+  });
+
   it("searches names, descriptions and keywords, in every language, and says when nothing matches", () => {
     renderScreen({
       decks: [capitals, { ...rivers, keywords: { en: ["water"], sv: ["vattendrag"] } }],
diff --git a/packages/ui/src/ui/LibraryScreen.tsx b/packages/ui/src/ui/LibraryScreen.tsx
index 245dcd26..0ff9ab23 100644
--- a/packages/ui/src/ui/LibraryScreen.tsx
+++ b/packages/ui/src/ui/LibraryScreen.tsx
@@ -3,7 +3,13 @@
 // SPDX-License-Identifier: MIT
 
 import { useEffect, useRef, useState } from "preact/hooks";
-import { filterLibraryDecks, topicsOf, type LibraryDeck } from "@solid-memo/domain/library";
+import {
+  filterLibraryDecks,
+  libraryCardLanguages,
+  topicsOf,
+  type LibraryDeck,
+} from "@solid-memo/domain/library";
+import { cardLanguageNames } from "./cardLanguageNames";
 import { ErrorMessage } from "./ErrorMessage";
 import { LibraryIcon } from "./icons";
 import { useI18n, type I18n, type ErrorText } from "./i18n";
@@ -30,10 +36,12 @@ export function forgetLibrarySelection(memoryKey: string): void {
 /**
  * The deck library: ready-made decks to copy into the current instance.
  * Any number can be checked and imported in one go. The list can be
- * narrowed to topics (checkboxes, from Solid Memo's topics scheme) and
- * by a search of names, descriptions and keywords, in every language
- * (filterLibraryDecks). A row says only the
- * deck's name and size; clicking it (anywhere but the checkbox and the
+ * narrowed to topics (checkboxes, from Solid Memo's topics scheme), to
+ * the languages the cards are in (checkboxes of those the decks state,
+ * a deck shown when its cards are in every one checked) and by a search
+ * of names, descriptions and keywords, in every language
+ * (filterLibraryDecks). A row says only the deck's name, its size and
+ * the languages of its cards; clicking it (anywhere but the checkbox and the
  * Preview button) opens the deck's own page, where it is described in
  * full and can be imported on its own. Preview tries its cards first.
  * A deck or course published elsewhere is added from a link to it
@@ -73,11 +81,12 @@ export function LibraryScreen({
   error: ErrorText | null;
   onImport: (decks: LibraryDeck[]) => void;
 }) {
-  const { t, tx } = useI18n();
+  const { t, tx, locale, languageParts } = useI18n();
   const [selectedUrls, setSelectedUrls] = useRemembered<string[]>(`${memoryKey}:selected`, []);
   const [topics, setTopics] = useRemembered<string[]>(`${memoryKey}:topics`, []);
+  const [languages, setLanguages] = useRemembered<string[]>(`${memoryKey}:languages`, []);
   const [query, setQuery] = useRemembered(`${memoryKey}:query`, "");
-  const shown = filterLibraryDecks(decks, { topics, query });
+  const shown = filterLibraryDecks(decks, { topics, languages, query });
   // A deck the filters hide stays checked for when it shows again, but is
   // not imported: the import never includes what the user cannot see. A
   // course is never imported: it is started from its page, and its cards
@@ -86,6 +95,9 @@ export function LibraryScreen({
     (deck) => deck.isCourse !== true && selectedUrls.includes(deck.url),
   );
   const available = topicsOf(decks);
+  const availableLanguages = libraryCardLanguages(decks)
+    .map((language) => ({ iri: language.iri, name: languageParts(language.tag).name }))
+    .sort((a, b) => a.name.localeCompare(b.name, locale));
   const count =
     shown.length === decks.length
       ? t("library.deckCount", { count: decks.length })
@@ -98,11 +110,11 @@ export function LibraryScreen({
     if (!filtered.current) return;
     const timer = setTimeout(() => setAnnounced(result), ANNOUNCE_DELAY_MS);
     return () => clearTimeout(timer);
-  }, [result, topics, query]);
+  }, [result, topics, languages, query]);
 
-  function toggleTopic(topic: string, checked: boolean) {
+  function toggleIn(set: typeof setTopics, value: string, checked: boolean) {
     filtered.current = true;
-    setTopics((current) => (checked ? [...current, topic] : current.filter((t) => t !== topic)));
+    set((current) => (checked ? [...current, value] : current.filter((one) => one !== value)));
   }
 
   function toggle(deck: LibraryDeck, checked: boolean) {
@@ -143,13 +155,30 @@ export function LibraryScreen({
                     <input
                       type="checkbox"
                       checked={topics.includes(topic.iri)}
-                      onChange={(e) => toggleTopic(topic.iri, e.currentTarget.checked)}
+                      onChange={(e) => toggleIn(setTopics, topic.iri, e.currentTarget.checked)}
                     />
                     <ReaderText text={topic.label} />
                   </label>
                 ))}
               </fieldset>
             )}
+            {availableLanguages.length > 0 && (
+              <fieldset class="library-languages">
+                <legend>{t("library.cardLanguages")}</legend>
+                {availableLanguages.map((language) => (
+                  <label key={language.iri} class="checkbox-option">
+                    <input
+                      type="checkbox"
+                      checked={languages.includes(language.iri)}
+                      onChange={(e) =>
+                        toggleIn(setLanguages, language.iri, e.currentTarget.checked)
+                      }
+                    />
+                    {language.name}
+                  </label>
+                ))}
+              </fieldset>
+            )}
             <label for="library-search">{t("library.search")}</label>
             <input
               id="library-search"
@@ -201,7 +230,8 @@ export function LibraryScreen({
 /**
  * One deck of the library's list (LibraryScreen): a box to check it (a
  * course has none, being started from its page), its name, linking to
- * its page, its size, that it is a course or already imported, and its
+ * its page, its size, the languages its cards are in, that it is a
+ * course or already imported, and its
  * Preview button. The Studio shows a draft's row as learners will see
  * it (docs/studio.md, The listing preview).
  */
@@ -222,7 +252,8 @@ export function LibraryDeckRow({
   previewHref: string;
   onToggle: (checked: boolean) => void;
 }) {
-  const { t, readerText } = useI18n();
+  const { t, readerText, languageParts } = useI18n();
+  const languages = cardLanguageNames(deck, languageParts);
   return (
     <>
       {/* A 44px target above the row's link, so a near miss
@@ -246,6 +277,9 @@ export function LibraryDeckRow({
       </a>
       <span class="library-deck-meta">
         <span class="hint">{t("common.cardCount", { count: deck.cardCount })}</span>
+        {languages.length > 0 && (
+          <span class="hint library-card-languages">{languages.join(", ")}</span>
+        )}
         {deck.isCourse === true && <span class="hint library-course">{t("library.course")}</span>}
         {imported && <span class="hint library-imported">{t("library.alreadyImported")}</span>}
       </span>
diff --git a/packages/ui/src/ui/Workspace.test.tsx b/packages/ui/src/ui/Workspace.test.tsx
index 9c4db87f..028ccb2b 100644
--- a/packages/ui/src/ui/Workspace.test.tsx
+++ b/packages/ui/src/ui/Workspace.test.tsx
@@ -802,6 +802,7 @@ describe("Workspace", () => {
       decks: [],
       deckCount: 0,
       cardCount: 0,
+      languages: [],
       reviewCount: 0,
       preferencesOutdated: outdated,
       instanceOutdated: false,
@@ -1212,6 +1213,7 @@ describe("Workspace", () => {
             ...firstRelease(deck.sourceUrl!),
             title: { en: "Capitals" },
             cardCount: 3,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1264,6 +1266,7 @@ describe("Workspace", () => {
             ...firstRelease(libraryUrl),
             title: { en: "Capitals" },
             cardCount: 3,
+            languages: [],
             authors: ["Anton Wiklund"],
             description: { en: "Every capital." },
             direction: "front-to-back" as const,
@@ -1320,6 +1323,7 @@ describe("Workspace", () => {
             ...firstRelease(libraryUrl),
             title: { en: "Capitals" },
             cardCount: 11,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1366,6 +1370,7 @@ describe("Workspace", () => {
             ...firstRelease(libraryUrl),
             title: { en: "Capitals" },
             cardCount: 1,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1414,6 +1419,7 @@ describe("Workspace", () => {
             ...firstRelease(libraryUrl),
             title: { en: "Capitals" },
             cardCount: 1,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1471,6 +1477,7 @@ describe("Workspace", () => {
             ...firstRelease(libraryUrl),
             title: { en: "Capitals" },
             cardCount: 1,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1508,6 +1515,7 @@ describe("Workspace", () => {
             ...firstRelease(libraryUrl),
             title: { en: "Capitals" },
             cardCount: 1,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1540,6 +1548,7 @@ describe("Workspace", () => {
       ...firstRelease(release),
       title: { en: "Pods" },
       cardCount: 2,
+      languages: [],
       authors: [],
       direction: "front-to-back" as const,
       sources: [],
@@ -1585,6 +1594,7 @@ describe("Workspace", () => {
       ...firstRelease(release),
       title: { en: "Rivers" },
       cardCount: 2,
+      languages: [],
       authors: [],
       direction: "front-to-back" as const,
       sources: [],
@@ -1642,6 +1652,7 @@ describe("Workspace", () => {
             ],
             title: { en: "Capitals" },
             cardCount: 3,
+            languages: [],
             authors: [],
             direction: "front-to-back" as const,
             sources: [],
@@ -1661,6 +1672,7 @@ describe("Workspace", () => {
       ...firstRelease(releaseUrl),
       title: { en: "Capitals" },
       cardCount: 3,
+      languages: [],
       authors: [],
       direction: "front-to-back" as const,
       sources: [],
diff --git a/packages/ui/src/ui/cardLanguageNames.ts b/packages/ui/src/ui/cardLanguageNames.ts
new file mode 100644
index 00000000..a8b845aa
--- /dev/null
+++ b/packages/ui/src/ui/cardLanguageNames.ts
@@ -0,0 +1,18 @@
+// SPDX-FileCopyrightText: 2026 Anton Wiklund and Solid Memo contributors
+//
+// SPDX-License-Identifier: MIT
+
+import { deckCardLanguages, type LibraryDeck } from "@solid-memo/domain/library";
+import type { I18n } from "./i18n";
+
+/**
+ * The languages a library deck's cards are in, each named in the app's
+ * language ("Swedish", "svenska"), in the deck's order: those the app
+ * knows (deckCardLanguages), none when the deck states none.
+ */
+export function cardLanguageNames(
+  deck: Pick<LibraryDeck, "languages">,
+  languageParts: I18n["languageParts"],
+): string[] {
+  return deckCardLanguages(deck).map((language) => languageParts(language.tag).name);
+}