Expose FS translation system to plugins

.changeset/chatty-jars-flash.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': minor
+---
+
+Adds a new [`HookParameters`](https://starlight.astro.build/reference/plugins/#hooks) utility type to get the type of a plugin hook’s arguments.

.changeset/large-balloons-compete.md

@@ -0,0 +1,29 @@
+---
+'@astrojs/starlight': minor
+---
+
+Exposes the built-in localization system in the Starlight plugin `config:setup` hook.
+
+⚠️ **BREAKING CHANGE:**
+
+This addition changes how Starlight plugins add or update translation strings used in Starlight’s localization APIs.
+Plugins previously using the [`injectTranslations()`](https://starlight.astro.build/reference/plugins/#injecttranslations) callback function from the plugin [`config:setup`](https://starlight.astro.build/reference/plugins/#configsetup) hook should now use the same function available in the [`i18n:setup`](https://starlight.astro.build/reference/plugins/#i18nsetup) hook.
+
+```diff
+export default {
+  name: 'plugin-with-translations',
+  hooks: {
+-   'config:setup'({ injectTranslations }) {
++   'i18n:setup'({ injectTranslations }) {
+      injectTranslations({
+        en: {
+          'myPlugin.doThing': 'Do the thing',
+        },
+        fr: {
+          'myPlugin.doThing': 'Faire le truc',
+        },
+      });
+    },
+  },
+};
+```

.changeset/loud-wolves-decide.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': minor
+---
+
+Adds a new [`useTranslations()`](https://starlight.astro.build/reference/plugins/#usetranslations) callback function to the Starlight plugin `config:setup` hook to generate a utility function to access UI strings for a given language.

.changeset/polite-fishes-remain.md

@@ -0,0 +1,21 @@
+---
+'@astrojs/starlight': minor
+---
+
+Deprecates the Starlight plugin `setup` hook in favor of the new `config:setup` hook which provides the same functionality.
+
+⚠️ **BREAKING CHANGE:**
+
+The Starlight plugin `setup` hook is now deprecated and will be removed in a future release. Please update your plugins to use the new `config:setup` hook instead.
+
+```diff
+export default {
+  name: 'plugin-with-translations',
+  hooks: {
+-   'setup'({ config }) {
++   'config:setup'({ config }) {
+      // Your plugin configuration setup code
+    },
+  },
+};
+```

.changeset/stupid-turkeys-appear.md

@@ -0,0 +1,11 @@
+---
+'@astrojs/starlight-docsearch': minor
+---
+
+⚠️ **BREAKING CHANGE:** The minimum supported version of Starlight is now 0.31.0
+
+Please use the `@astrojs/upgrade` command to upgrade your project:
+
+```sh
+npx @astrojs/upgrade
+```

.changeset/wet-cherries-try.md

@@ -0,0 +1,5 @@
+---
+'@astrojs/starlight': minor
+---
+
+Adds a new [`absolutePathToLang()`](https://starlight.astro.build/reference/plugins/#absolutepathtolang) callback function to the Starlight plugin `config:setup` to get the language for a given absolute file path.

docs/src/content/docs/guides/i18n.mdx

@@ -299,6 +299,9 @@ export const GET = (context) => {
 };
 ```
 
+In the context of a Starlight plugin, you can use the [`useTranslations()`](/reference/plugins/#usetranslations) helper to access this API for a specific language.
+See the [plugins reference](/reference/plugins/) for more information.
+
 ### Rendering a UI string
 
 Render UI strings using the `locals.t()` function.

docs/src/content/docs/reference/plugins.md

@@ -19,15 +19,21 @@ See below for details of the different properties and hook parameters.
 interface StarlightPlugin {
   name: string;
   hooks: {
-    setup: (options: {
+    'i18n:setup'?: (options: {
+      injectTranslations: (
+        translations: Record<string, Record<string, string>>
+      ) => void;
+    }) => void | Promise<void>;
+    'config:setup': (options: {
       config: StarlightUserConfig;
       updateConfig: (newConfig: StarlightUserConfig) => void;
       addIntegration: (integration: AstroIntegration) => void;
       astroConfig: AstroConfig;
       command: 'dev' | 'build' | 'preview';
       isRestart: boolean;
       logger: AstroIntegrationLogger;
-      injectTranslations: (Record<string, Record<string, string>>) => void;
+      useTranslations: (lang: string) => I18nT;
+      absolutePathToLang: (path: string) => string;
     }) => void | Promise<void>;
   };
 }
@@ -41,12 +47,100 @@ A plugin must provide a unique name that describes it. The name is used when [lo
 
 ## `hooks`
 
-Hooks are functions which Starlight calls to run plugin code at specific times. Currently, Starlight supports a single `setup` hook.
+Hooks are functions which Starlight calls to run plugin code at specific times.
+
+To get the type of a hook's arguments, use the `HookParameters` utility type and pass in the hook name.
+In the following example, the `options` parameter is typed to match the arguments passed to the `config:setup` hook:
+
+```ts
+import type { HookParameters } from '@astrojs/starlight/types';
+
+function configSetup(options: HookParameters['config:setup']) {
+  options.useTranslations('en');
+}
+```
+
+### `i18n:setup`
+
+Plugin internationalization setup function called when Starlight is initialized.
+The `i18n:setup` hook can be used to inject translation strings so a plugin can support different locales.
+These translations will be available via [`useTranslations()`](#usetranslations) in the `config:setup` hook and in UI components via [`Astro.locals.t()`](/guides/i18n/#using-ui-translations).
+
+The `i18n:setup` hook is called with the following options:
+
+#### `injectTranslations`
+
+**type:** `(translations: Record<string, Record<string, string>>) => void`
+
+A callback function to add or update translation strings used in Starlight’s [localization APIs](/guides/i18n/#using-ui-translations).
+
+In the following example, a plugin injects translations for a custom UI string named `myPlugin.doThing` for the `en` and `fr` locales:
+
+```ts {6-13} /(injectTranslations)[^(]/
+// plugin.ts
+export default {
+  name: 'plugin-with-translations',
+  hooks: {
+    'i18n:setup'({ injectTranslations }) {
+      injectTranslations({
+        en: {
+          'myPlugin.doThing': 'Do the thing',
+        },
+        fr: {
+          'myPlugin.doThing': 'Faire le truc',
+        },
+      });
+    },
+  },
+};
+```
+
+To use the injected translations in your plugin UI, follow the [“Using UI translations” guide](/guides/i18n/#using-ui-translations).
+If you need to use UI strings in the context of the [`config:setup`](#configsetup) hook of your plugin, you can use the [`useTranslations()`](#usetranslations) callback.
+
+Types for a plugin’s injected translation strings are generated automatically in a user’s project, but are not yet available when working in your plugin’s codebase.
+To type the `locals.t` object in the context of your plugin, declare the following global namespaces in a TypeScript declaration file:
+
+```ts
+// env.d.ts
+declare namespace App {
+  type StarlightLocals = import('@astrojs/starlight').StarlightLocals;
+  // Define the `locals.t` object in the context of a plugin.
+  interface Locals extends StarlightLocals {}
+}
+
+declare namespace StarlightApp {
+  // Define the additional plugin translations in the `I18n` interface.
+  interface I18n {
+    'myPlugin.doThing': string;
+  }
+}
+```
+
+You can also infer the types for the `StarlightApp.I18n` interface from a source file if you have an object containing your translations.
+
+For example, given the following source file:
+
+```ts title="ui-strings.ts"
+export const UIStrings = {
+  en: { 'myPlugin.doThing': 'Do the thing' },
+  fr: { 'myPlugin.doThing': 'Faire le truc' },
+};
+```
+
+The following declaration would infer types from the English keys in the source file:
+
+```ts title="env.d.ts"
+declare namespace StarlightApp {
+  type UIStrings = typeof import('./ui-strings').UIStrings.en;
+  interface I18n extends UIStrings {}
+}
+```
 
-### `hooks.setup`
+### `config:setup`
 
-Plugin setup function called when Starlight is initialized (during the [`astro:config:setup`](https://docs.astro.build/en/reference/integrations-reference/#astroconfigsetup) integration hook).
-The `setup` hook can be used to update the Starlight configuration or add Astro integrations.
+Plugin configuration setup function called when Starlight is initialized (during the [`astro:config:setup`](https://docs.astro.build/en/reference/integrations-reference/#astroconfigsetup) integration hook).
+The `config:setup` hook can be used to update the Starlight configuration or add Astro integrations.
 
 This hook is called with the following options:
 
@@ -73,7 +167,7 @@ In the following example, a new [`social`](/reference/configuration/#social) med
 export default {
   name: 'add-twitter-plugin',
   hooks: {
-    setup({ config, updateConfig }) {
+    'config:setup'({ config, updateConfig }) {
       updateConfig({
         social: {
           ...config.social,
@@ -100,7 +194,7 @@ import react from '@astrojs/react';
 export default {
   name: 'plugin-using-react',
   hooks: {
-    setup({ addIntegration, astroConfig }) {
+    'config:setup'({ addIntegration, astroConfig }) {
       const isReactLoaded = astroConfig.integrations.find(
         ({ name }) => name === '@astrojs/react'
       );
@@ -149,7 +243,7 @@ All logged messages will be prefixed with the plugin name.
 export default {
   name: 'long-process-plugin',
   hooks: {
-    setup({ logger }) {
+    'config:setup'({ logger }) {
       logger.info('Starting long process…');
       // Some long process…
     },
@@ -163,70 +257,78 @@ The example above will log a message that includes the provided info message:
 [long-process-plugin] Starting long process…
 ```
 
-#### `injectTranslations`
-
-**type:** `(translations: Record<string, Record<string, string>>) => void`
+#### `useTranslations`
 
-A callback function to add or update translation strings used in Starlight’s [localization APIs](/guides/i18n/#using-ui-translations).
+**type:** `(lang: string) => I18nT`
 
-In the following example, a plugin injects translations for a custom UI string named `myPlugin.doThing` for the `en` and `fr` locales:
+Call `useTranslations()` with a BCP-47 language tag to generate a utility function that provides access to UI strings for that language.
+`useTranslations()` returns an equivalent of the `Astro.locals.t()` API that is available in Astro components.
+To learn more about the available APIs, see the [“Using UI translations”](/guides/i18n/#using-ui-translations) guide.
 
-```ts {6-13} /(injectTranslations)[^(]/
+```ts {6}
 // plugin.ts
 export default {
-  name: 'plugin-with-translations',
+  name: 'plugin-use-translations',
   hooks: {
-    setup({ injectTranslations }) {
-      injectTranslations({
-        en: {
-          'myPlugin.doThing': 'Do the thing',
-        },
-        fr: {
-          'myPlugin.doThing': 'Faire le truc',
-        },
-      });
+    'config:setup'({ useTranslations, logger }) {
+      const t = useTranslations('zh-CN');
+      logger.info(t('builtWithStarlight.label'));
     },
   },
 };
 ```
 
-To use the injected translations in your plugin UI, follow the [“Using UI translations” guide](/guides/i18n/#using-ui-translations).
+The example above will log a message that includes a built-in UI string for the Simplified Chinese language:
 
-Types for a plugin’s injected translation strings are generated automatically in a user’s project, but are not yet available when working in your plugin’s codebase.
-To type the `locals.t` object in the context of your plugin, declare the following global namespaces in a TypeScript declaration file:
+```shell
+[plugin-use-translations] 基于 Starlight 构建
+```
 
-```ts
-// env.d.ts
-declare namespace App {
-  type StarlightLocals = import('@astrojs/starlight').StarlightLocals;
-  // Define the `locals.t` object in the context of a plugin.
-  interface Locals extends StarlightLocals {}
-}
+#### `absolutePathToLang`
 
-declare namespace StarlightApp {
-  // Define the additional plugin translations in the `I18n` interface.
-  interface I18n {
-    'myPlugin.doThing': string;
-  }
-}
-```
+**type:** `(path: string) => string`
 
-You can also infer the types for the `StarlightApp.I18n` interface from a source file if you have an object containing your translations.
+Call `absolutePathToLang()` with an absolute file path to get the language for that file.
 
-For example, given the following source file:
+This can be particularly useful when adding [remark or rehype plugins](https://docs.astro.build/en/guides/markdown-content/#markdown-plugins) to process Markdown or MDX files.
+The [virtual file format](https://github.com/vfile/vfile) used by these plugins includes the [absolute path](https://github.com/vfile/vfile#filepath) of the file being processed, which can be used with `absolutePathToLang()` to determine the language of the file.
+The returned language can be used with the [`useTranslations()`](#usetranslations) helper to get UI strings for that language.
 
-```ts title="ui-strings.ts"
-export const UIStrings = {
-  en: { 'myPlugin.doThing': 'Do the thing' },
-  fr: { 'myPlugin.doThing': 'Faire le truc' },
+For example, given the following Starlight configuration:
+
+```js
+starlight({
+  title: 'My Docs',
+  defaultLocale: 'en',
+  locales: {
+    // English docs in `src/content/docs/en/`
+    en: { label: 'English' },
+    // French docs in `src/content/docs/fr/`
+    fr: { label: 'Français', lang: 'fr' },
+  },
+});
+```
+
+A plugin can determine the language of a file using its absolute path:
+
+```ts {6-8} /fr/
+// plugin.ts
+export default {
+  name: 'plugin-use-translations',
+  hooks: {
+    'config:setup'({ absolutePathToLang, useTranslations, logger }) {
+      const lang = absolutePathToLang(
+        '/absolute/path/to/project/src/content/docs/fr/index.mdx'
+      );
+      const t = useTranslations(lang);
+      logger.info(t('aside.tip'));
+    },
+  },
 };
 ```
 
-The following declaration would infer types from the English keys in the source file:
+The example above will log a message that includes a built-in UI string for the French language:
 
-```ts title="env.d.ts"
-declare namespace StarlightApp {
-  type UIStrings = typeof import('./ui-strings').UIStrings.en;
-  interface I18n extends UIStrings {}
-}
+```shell
+[plugin-use-translations] Astuce
 ```

packages/docsearch/index.ts

@@ -48,7 +48,7 @@ export default function starlightDocSearch(userConfig: DocSearchUserConfig): Sta
 	return {
 		name: 'starlight-docsearch',
 		hooks: {
-			setup({ addIntegration, config, logger, updateConfig }) {
+			'config:setup'({ addIntegration, config, logger, updateConfig }) {
 				// If the user has already has a custom override for the Search component, don't override it.
 				if (config.components?.Search) {
 					logger.warn(