Fix language string normalisation (#960)

Fixes #948

src/frontend/src/tests/languageFilters.test.ts

@@ -4,7 +4,9 @@ import type { Language } from '../types/index';
 import {
   LANGUAGE_OPTION_ALL,
   LANGUAGE_OPTION_DEFAULT,
+  buildLanguageNormalizer,
   getReleaseSearchLanguageParams,
+  releaseLanguageMatchesFilter,
 } from '../utils/languageFilters';
 
 const supportedLanguages: Language[] = [
@@ -35,4 +37,33 @@ describe('languageFilters release search params', () => {
 
     expect(result).toEqual(['de', 'hu']);
   });
+
+  it('normalizes legacy default language names when combined with explicit filters', () => {
+    const result = getReleaseSearchLanguageParams(
+      [LANGUAGE_OPTION_DEFAULT, 'de'],
+      supportedLanguages,
+      ['english'],
+    );
+
+    expect(result).toEqual(['en', 'de']);
+  });
+});
+
+describe('releaseLanguageMatchesFilter', () => {
+  it('matches release language names against legacy default language names', () => {
+    const normalizer = buildLanguageNormalizer(supportedLanguages);
+
+    expect(releaseLanguageMatchesFilter('English', ['english'], normalizer)).toBe(true);
+  });
+
+  it('keeps English-only issue 948 fallback results with a legacy English default', () => {
+    const normalizer = buildLanguageNormalizer(supportedLanguages);
+    const issue948Languages = [...Array<string>(48).fill('en'), 'de, en', 'en, es'];
+
+    const visibleLanguages = issue948Languages.filter((language) =>
+      releaseLanguageMatchesFilter(language, ['english'], normalizer),
+    );
+
+    expect(visibleLanguages).toHaveLength(48);
+  });
 });

src/frontend/src/utils/languageFilters.ts

@@ -48,8 +48,11 @@ export const getLanguageFilterValues = (
     return null;
   }
 
-  const supportedCodes = new Set(supportedLanguages.map((lang) => lang.code));
-  const defaultCodes = defaultLanguageCodes.filter((code) => supportedCodes.has(code));
+  const languageNormalizer = buildLanguageNormalizer(supportedLanguages);
+  const supportedCodes = new Set(supportedLanguages.map((lang) => lang.code.toLowerCase()));
+  const defaultCodes = defaultLanguageCodes
+    .map((code) => languageNormalizer.get(code.toLowerCase()) ?? code.toLowerCase())
+    .filter((code) => supportedCodes.has(code));
   const resolved = new Set<string>();
 
   uniqueSelection.forEach((code) => {
@@ -58,8 +61,9 @@ export const getLanguageFilterValues = (
       return;
     }
 
-    if (supportedCodes.has(code)) {
-      resolved.add(code);
+    const normalizedCode = languageNormalizer.get(code.toLowerCase()) ?? code.toLowerCase();
+    if (supportedCodes.has(normalizedCode)) {
+      resolved.add(normalizedCode);
     }
   });
 
@@ -130,6 +134,11 @@ export const releaseLanguageMatchesFilter = (
     return part;
   });
 
-  const selectedSet = new Set(selectedCodes.map((c) => c.toLowerCase()));
+  const selectedSet = new Set(
+    selectedCodes.map((code) => {
+      const normalizedCode = code.toLowerCase();
+      return languageNormalizer?.get(normalizedCode) ?? normalizedCode;
+    }),
+  );
   return releaseCodes.every((code) => selectedSet.has(code));
 };