From f7bc228aa9eebba2bc11e0aa63571800f54515e8 Mon Sep 17 00:00:00 2001
From: mario ma <mario.ma.node@gmail.com>
Date: Wed, 3 Dec 2025 11:59:59 +0800
Subject: [PATCH] feat: Support to set defaultLanguage and availableLanguages
 in new frontend system

Signed-off-by: mario ma <mario.ma.node@gmail.com>
---
 .changeset/gentle-singers-love.md            |  5 ++++
 packages/app-next/app-config.yaml            |  5 ++++
 plugins/app/report.api.md                    | 22 +++++++++++++---
 plugins/app/src/extensions/AppLanguageApi.ts | 27 +++++++++++++++-----
 4 files changed, 48 insertions(+), 11 deletions(-)
 create mode 100644 .changeset/gentle-singers-love.md

diff --git a/.changeset/gentle-singers-love.md b/.changeset/gentle-singers-love.md
new file mode 100644
index 0000000000..0fb2dbc047
--- /dev/null
+++ b/.changeset/gentle-singers-love.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-app': patch
+---
+
+Support to set defaultLanguage and availableLanguages in new frontend system
diff --git a/packages/app-next/app-config.yaml b/packages/app-next/app-config.yaml
index dcaddfb9bf..1121cfc0d5 100644
--- a/packages/app-next/app-config.yaml
+++ b/packages/app-next/app-config.yaml
@@ -21,6 +21,11 @@ app:
         ownerEntityRefs: [cubic-belugas]
 
   extensions:
+    # set availableLanguages example
+    - api:app/app-language:
+        config:
+          availableLanguages: ['en', 'es', 'fr', 'de', 'ja']
+          defaultLanguage: 'en'
     - entity-card:org/members-list:
         config:
           showAggregateMembersToggle: true
diff --git a/plugins/app/report.api.md b/plugins/app/report.api.md
index 313d09cfee..c9aa1cf9f7 100644
--- a/plugins/app/report.api.md
+++ b/plugins/app/report.api.md
@@ -232,12 +232,26 @@ const appPlugin: OverridableFrontendPlugin<
       ) => ExtensionBlueprintParams<AnyApiFactory>;
     }>;
     'api:app/app-language': OverridableExtensionDefinition<{
+      config: {
+        defaultLanguage: string | undefined;
+        availableLanguages: string[] | undefined;
+      };
+      configInput: {
+        defaultLanguage?: string | undefined;
+        availableLanguages?: string[] | undefined;
+      };
+      output: ExtensionDataRef<AnyApiFactory, 'core.api.factory', {}>;
+      inputs: {
+        [x: string]: ExtensionInput<
+          ExtensionDataRef,
+          {
+            singleton: boolean;
+            optional: boolean;
+          }
+        >;
+      };
       kind: 'api';
       name: 'app-language';
-      config: {};
-      configInput: {};
-      output: ExtensionDataRef<AnyApiFactory, 'core.api.factory', {}>;
-      inputs: {};
       params: <
         TApi,
         TImpl extends TApi,
diff --git a/plugins/app/src/extensions/AppLanguageApi.ts b/plugins/app/src/extensions/AppLanguageApi.ts
index 325dffa2fd..4f605aa30f 100644
--- a/plugins/app/src/extensions/AppLanguageApi.ts
+++ b/plugins/app/src/extensions/AppLanguageApi.ts
@@ -19,12 +19,25 @@ import { AppLanguageSelector } from '../../../../packages/core-app-api/src/apis/
 import { appLanguageApiRef } from '@backstage/core-plugin-api/alpha';
 import { ApiBlueprint } from '@backstage/frontend-plugin-api';
 
-export const AppLanguageApi = ApiBlueprint.make({
+export const AppLanguageApi = ApiBlueprint.makeWithOverrides({
   name: 'app-language',
-  params: defineParams =>
-    defineParams({
-      api: appLanguageApiRef,
-      deps: {},
-      factory: () => AppLanguageSelector.createWithStorage(),
-    }),
+  config: {
+    schema: {
+      defaultLanguage: z => z.string().optional(),
+      availableLanguages: z => z.array(z.string()).optional(),
+    },
+  },
+  factory(originalFactory, { config }) {
+    return originalFactory(defineParams =>
+      defineParams({
+        api: appLanguageApiRef,
+        deps: {},
+        factory: () =>
+          AppLanguageSelector.createWithStorage({
+            defaultLanguage: config.defaultLanguage,
+            availableLanguages: config.availableLanguages,
+          }),
+      }),
+    );
+  },
 });