Support translations in sidebar config (#95)

6 files changed, 96 insertions, 41 deletions

diff --git a/.changeset/calm-buttons-wink.md b/.changeset/calm-buttons-wink.md
new file mode 100644
index 00000000..22be7e42
--- /dev/null
+++ b/.changeset/calm-buttons-wink.md
@@ -0,0 +1,5 @@
+---
+"@astrojs/starlight": patch
+---
+
+Support translations in sidebar config
diff --git a/docs/astro.config.mjs b/docs/astro.config.mjs
index c81072e1..b64d8383 100644
--- a/docs/astro.config.mjs
+++ b/docs/astro.config.mjs
@@ -30,22 +30,14 @@ export default defineConfig({
         },
       ],
       locales: {
-        root: {
-          label: 'English',
-          lang: 'en',
-        },
-        de: {
-          label: 'Deutsch',
-          lang: 'de',
-        },
-        es: {
-          label: 'Español',
-          lang: 'es',
-        }
+        root: { label: 'English', lang: 'en' },
+        de: { label: 'Deutsch', lang: 'de' },
+        es: { label: 'Español', lang: 'es' },
       },
       sidebar: [
         {
           label: 'Start Here',
+          translations: { de: 'Beginne hier', es: 'Comienza aqui' },
           items: [
             { label: 'Welcome, world', link: '/' },
             { label: 'Getting Started', link: 'getting-started' },
@@ -54,15 +46,13 @@ export default defineConfig({
         },
         {
           label: 'Guides',
-          autogenerate: {
-            directory: 'guides',
-          },
+          translations: { de: 'Anleitungen', es: 'Guías' },
+          autogenerate: { directory: 'guides' },
         },
         {
           label: 'Reference',
-          autogenerate: {
-            directory: 'reference',
-          },
+          translations: { de: 'Referenz', es: 'Referencias' },
+          autogenerate: { directory: 'reference' },
         },
       ],
     }),
diff --git a/docs/src/content/docs/reference/configuration.md b/docs/src/content/docs/reference/configuration.md
index 06381c86..4413311d 100644
--- a/docs/src/content/docs/reference/configuration.md
+++ b/docs/src/content/docs/reference/configuration.md
@@ -89,18 +89,42 @@ starlight({
     // A group linking to all pages in the reference directory.
     {
       label: 'Reference',
-      autogenerate: {
-        directory: 'reference',
-      },
+      autogenerate: { directory: 'reference' },
     },
   ],
 });
 ```
 
-:::note[Sorting]
+#### Sorting
+
 Autogenerated sidebar groups are sorted by filename alphabetically.
 For example, a page generated from `astro.md` would appear above the page for `starlight.md`.
-:::
+
+#### Translating labels
+
+If your site is multilingual, each item’s `label` is considered to be in the default locale. You can set a `translations` property to provide labels for your other supported languages:
+
+```js
+sidebar: [
+  // An example sidebar with labels translated to French.
+  {
+    label: 'Start Here',
+    translations: { fr: 'Commencez ici' },
+    items: [
+      {
+        label: 'Getting Started',
+        translations: { fr: 'Bien démarrer' },
+        link: '/getting-started',
+      },
+      {
+        label: 'Project Structure',
+        translations: { fr: 'Structure du projet' },
+        link: '/structure',
+      },
+    ],
+  },
+];
+```
 
 #### `SidebarGroup`
 
@@ -108,10 +132,12 @@ For example, a page generated from `astro.md` would appear above the page for `s
 type SidebarGroup =
   | {
       label: string;
+      translations?: Record<string, string>;
       items: Array<LinkItem | SidebarGroup>;
     }
   | {
       label: string;
+      translations?: Record<string, string>;
       autogenerate: {
         directory: string;
       };
diff --git a/packages/starlight/utils/i18n.ts b/packages/starlight/utils/i18n.ts
new file mode 100644
index 00000000..2dd43c3b
--- /dev/null
+++ b/packages/starlight/utils/i18n.ts
@@ -0,0 +1,16 @@
+/**
+ * Get the string for the passed language from a dictionary object.
+ *
+ * TODO: Make this clever. Currently a simple key look-up, but should use
+ * BCP-47 mapping so that e.g. `en-US` returns `en` strings, and use the
+ * site’s default locale as a last resort.
+ *
+ * @example
+ * pickLang({ en: 'Hello', fr: 'Bonjour' }, 'en'); // => 'Hello'
+ */
+export function pickLang<T extends Record<string, string>>(
+  dictionary: T,
+  lang: keyof T
+): string | undefined {
+  return dictionary[lang];
+}
diff --git a/packages/starlight/utils/navigation.ts b/packages/starlight/utils/navigation.ts
index e7e6a91e..bcdf79cf 100644
--- a/packages/starlight/utils/navigation.ts
+++ b/packages/starlight/utils/navigation.ts
@@ -1,8 +1,9 @@
 import { basename, dirname } from 'node:path';
 import config from 'virtual:starlight/user-config';
 import { withBase } from './base';
+import { pickLang } from './i18n';
 import { Route, getLocaleRoutes, routes } from './routing';
-import { slugToPathname } from './slugs';
+import { localeToLang, slugToPathname } from './slugs';
 import type {
   AutoSidebarGroup,
   SidebarItem,
@@ -48,7 +49,7 @@ function configItemToEntry(
   } else {
     return {
       type: 'group',
-      label: item.label,
+      label: pickLang(item.translations, localeToLang(locale)) || item.label,
       entries: item.items.map((i) =>
         configItemToEntry(i, currentPathname, locale, routes)
       ),
@@ -75,7 +76,7 @@ function groupFromAutogenerateConfig(
   const tree = treeify(dirDocs, localeDir);
   return {
     type: 'group',
-    label: item.label,
+    label: pickLang(item.translations, localeToLang(locale)) || item.label,
     entries: sidebarFromDir(tree, currentPathname, locale),
   };
 }
@@ -102,7 +103,8 @@ function linkFromConfig(
     // Inject current locale into link.
     if (locale) href = '/' + locale + href;
   }
-  return makeLink(href, item.label, currentPathname);
+  const label = pickLang(item.translations, localeToLang(locale)) || item.label;
+  return makeLink(href, label, currentPathname);
 }
 
 /** Create a link entry. */
diff --git a/packages/starlight/utils/user-config.ts b/packages/starlight/utils/user-config.ts
index 9aea7325..bca6cfff 100644
--- a/packages/starlight/utils/user-config.ts
+++ b/packages/starlight/utils/user-config.ts
@@ -27,17 +27,20 @@ const LocaleSchema = z.object({
     ),
 });
 
-const SidebarLinkItemSchema = z.object({
+const SidebarBaseSchema = z.object({
   /** The visible label for this item in the sidebar. */
   label: z.string(),
+  /** Translations of the `label` for each supported language. */
+  translations: z.record(z.string()).default({}),
+});
+
+const SidebarLinkItemSchema = SidebarBaseSchema.extend({
   /** The link to this item’s content. Can be a relative link to local files or the full URL of an external page. */
   link: z.string(),
 });
 export type SidebarLinkItem = z.infer<typeof SidebarLinkItemSchema>;
 
-const AutoSidebarGroupSchema = z.object({
-  /** The visible label for this item in the sidebar. */
-  label: z.string(),
+const AutoSidebarGroupSchema = SidebarBaseSchema.extend({
   /** Enable autogenerating a sidebar category from a specific docs directory. */
   autogenerate: z.object({
     /** The directory to generate sidebar items for. */
@@ -49,20 +52,29 @@ const AutoSidebarGroupSchema = z.object({
 });
 export type AutoSidebarGroup = z.infer<typeof AutoSidebarGroupSchema>;
 
-type ManualSidebarGroup = {
-  /** The visible label for this item in the sidebar. */
-  label: string;
+type ManualSidebarGroupInput = z.input<typeof SidebarBaseSchema> & {
   /** Array of links and subcategories to display in this category. */
   items: Array<
-    | SidebarLinkItem
-    | z.infer<typeof AutoSidebarGroupSchema>
-    | ManualSidebarGroup
+    | z.input<typeof SidebarLinkItemSchema>
+    | z.input<typeof AutoSidebarGroupSchema>
+    | ManualSidebarGroupInput
   >;
 };
 
-const ManualSidebarGroupSchema: z.ZodType<ManualSidebarGroup> = z.object({
-  /** The visible label for this item in the sidebar. */
-  label: z.string(),
+type ManualSidebarGroupOutput = z.output<typeof SidebarBaseSchema> & {
+  /** Array of links and subcategories to display in this category. */
+  items: Array<
+    | z.output<typeof SidebarLinkItemSchema>
+    | z.output<typeof AutoSidebarGroupSchema>
+    | ManualSidebarGroupOutput
+  >;
+};
+
+const ManualSidebarGroupSchema: z.ZodType<
+  ManualSidebarGroupOutput,
+  z.ZodTypeDef,
+  ManualSidebarGroupInput
+> = SidebarBaseSchema.extend({
   /** Array of links and subcategories to display in this category. */
   items: z.lazy(() =>
     z
@@ -83,7 +95,11 @@ const SidebarItemSchema = z.union([
 export type SidebarItem = z.infer<typeof SidebarItemSchema>;
 
 const SidebarGroupSchema: z.ZodType<
-  ManualSidebarGroup | z.infer<typeof AutoSidebarGroupSchema>
+  | z.output<typeof ManualSidebarGroupSchema>
+  | z.output<typeof AutoSidebarGroupSchema>,
+  z.ZodTypeDef,
+  | z.input<typeof ManualSidebarGroupSchema>
+  | z.input<typeof AutoSidebarGroupSchema>
 > = z.union([ManualSidebarGroupSchema, AutoSidebarGroupSchema]);
 
 const UserConfigSchema = z.object({