diff --git a/src/modules/core/utils/Languages.ts b/src/modules/core/utils/Languages.ts
index 3d5387ec..ffe23941 100644
--- a/src/modules/core/utils/Languages.ts
+++ b/src/modules/core/utils/Languages.ts
@@ -75,6 +75,10 @@ export const toUniqueLanguageCodes = (codes: string[]): string[] => {
         .map(([, languagesOfIsoCode]) => languagesOfIsoCode![0].orgCode);
 };
 
+export const toComparableLanguage = (code: string): string => getLanguage(code).isoCode;
+
+export const toComparableLanguages = (codes: string[]): string[] => codes.map(toComparableLanguage);
+
 function defaultNativeLang(): readonly string[] {
     const preferredLanguages = toUniqueLanguageCodes([...navigator.languages]);
 
diff --git a/src/modules/extension/Extensions.utils.ts b/src/modules/extension/Extensions.utils.ts
index a8ec989d..aafaef4e 100644
--- a/src/modules/extension/Extensions.utils.ts
+++ b/src/modules/extension/Extensions.utils.ts
@@ -15,7 +15,14 @@ import {
     InstalledState,
     TExtension,
 } from '@/modules/extension/Extensions.types.ts';
-import { DefaultLanguage, langCodeToName, langSortCmp } from '@/modules/core/utils/Languages.ts';
+import {
+    DefaultLanguage,
+    langCodeToName,
+    langSortCmp,
+    toComparableLanguage,
+    toComparableLanguages,
+    toUniqueLanguageCodes,
+} from '@/modules/core/utils/Languages.ts';
 import { extensionLanguageToTranslationKey } from '@/modules/extension/Extensions.constants.ts';
 import { enhancedCleanup } from '@/util/Strings.ts';
 
@@ -98,8 +105,14 @@ export const filterExtensions = (
     selectedLanguages: string[],
     showNsfw: boolean,
     query: string | null | undefined,
-): TExtension[] =>
-    extensions
-        .filter((extension) => selectedLanguages.includes(extension.lang) || extension.isInstalled)
+): TExtension[] => {
+    const normalizedSelectedLanguages = toComparableLanguages(toUniqueLanguageCodes(selectedLanguages));
+
+    return extensions
+        .filter(
+            (extension) =>
+                normalizedSelectedLanguages.includes(toComparableLanguage(extension.lang)) || extension.isInstalled,
+        )
         .filter((extension) => showNsfw || !extension.isNsfw)
         .filter((extension) => !query || enhancedCleanup(extension.name).includes(enhancedCleanup(query)));
+};
diff --git a/src/modules/source/services/Sources.ts b/src/modules/source/services/Sources.ts
index b57d4833..31a03ef0 100644
--- a/src/modules/source/services/Sources.ts
+++ b/src/modules/source/services/Sources.ts
@@ -13,7 +13,13 @@ import {
     SourceNsfwInfo,
     SourceRepoInfo,
 } from '@/modules/source/Source.types.ts';
-import { DefaultLanguage, langSortCmp } from '@/modules/core/utils/Languages.ts';
+import {
+    DefaultLanguage,
+    langSortCmp,
+    toComparableLanguage,
+    toComparableLanguages,
+    toUniqueLanguageCodes,
+} from '@/modules/core/utils/Languages.ts';
 
 export class Sources {
     static readonly LOCAL_SOURCE_ID = '0';
@@ -55,12 +61,14 @@ export class Sources {
             keepLocalSource,
         }: { showNsfw?: boolean; languages?: string[]; keepLocalSource?: boolean } = {},
     ): Source[] {
+        const normalizedLanguages = toComparableLanguages(toUniqueLanguageCodes(languages ?? []));
+
         return sources
             .filter((source) => showNsfw || !source.isNsfw || (keepLocalSource && Sources.isLocalSource(source)))
             .filter(
                 (source) =>
                     !languages ||
-                    languages.includes(Sources.getLanguage(source)) ||
+                    normalizedLanguages.includes(toComparableLanguage(Sources.getLanguage(source))) ||
                     (keepLocalSource && Sources.isLocalSource(source)),
             );
     }