Port detect-language.js to TypeScript (#50623)

src/types.ts

@@ -10,5 +10,19 @@ export type ExtendedRequest = Request & {
     currentCategory?: string
     error?: Error
   }
+  language?: string
+  userLanguage?: string
   // Add more properties here as needed
 }
+
+type Language = {
+  name: string
+  code: string
+  hreflang: string
+  dir: string
+  wip: boolean
+}
+
+export type Languages = {
+  [key: string]: Language
+}