feat(translation): expose sourceLang in article responses regardless of translation match

Previously TranslationResult only included translationMeta (and thus sourceLang) when a translation was applied. When the requested locale had no translation entry, the backend served the source content as fallback but omitted any indication of what language that source was — leaving clients unable to display accurate language metadata for fallback content.

getTranslationAndAvailableLanguages now also returns sourceLang (read from any translation entry, since they all share the same source). translateArticle surfaces it as a top-level field on TranslationResult, populated in both the matched and no-match branches. The three article controllers (note/post/page) pass it through to the response.

Author: Innei

apps/core/src/modules/ai/ai-translation/ai-translation.service.ts

@@ -1275,6 +1275,7 @@ export class AiTranslationService
     options?: { ignoreVisibility?: boolean },
   ): Promise<{
     availableTranslations: string[]
+    sourceLang: string | null
     translation: AITranslationModel | null
   }> {
     const article = await this.databaseService.findGlobalById(articleId)
@@ -1295,9 +1296,11 @@ export class AiTranslationService
       .select('hash lang sourceLang sourceModified created')
 
     if (!translations.length) {
-      return { availableTranslations: [], translation: null }
+      return { availableTranslations: [], sourceLang: null, translation: null }
     }
 
+    const sourceLang = translations[0]?.sourceLang ?? null
+
     const snapshot = this.buildSnapshotFromDocument(articleId, document)
     const validLangs: string[] = []
     const staleLangs: string[] = []
@@ -1341,6 +1344,7 @@ export class AiTranslationService
 
     return {
       availableTranslations: validLangs,
+      sourceLang,
       translation: matchedTranslation,
     }
   }

apps/core/src/modules/note/note.controller.ts

@@ -126,6 +126,7 @@ export class NoteController {
         contentFormat: translationResult.contentFormat,
       }),
       isTranslated: translationResult.isTranslated,
+      sourceLang: translationResult.sourceLang,
       translationMeta: translationResult.translationMeta,
       availableTranslations: translationResult.availableTranslations,
       hasInsightsInLocale,
@@ -606,6 +607,7 @@ export class NoteController {
           contentFormat: translationResult.contentFormat,
         }),
         isTranslated: translationResult.isTranslated,
+        sourceLang: translationResult.sourceLang,
         translationMeta: translationResult.translationMeta,
         availableTranslations: translationResult.availableTranslations,
         hasInsightsInLocale,

apps/core/src/modules/page/page.controller.ts

@@ -194,6 +194,7 @@ export class PageController {
           contentFormat: translationResult.contentFormat,
         }),
         isTranslated: translationResult.isTranslated,
+        sourceLang: translationResult.sourceLang,
         translationMeta: translationResult.translationMeta,
         availableTranslations: translationResult.availableTranslations,
       },

apps/core/src/modules/post/post.controller.ts

@@ -374,6 +374,7 @@ export class PostController {
           contentFormat: translationResult.contentFormat,
         }),
         isTranslated: translationResult.isTranslated,
+        sourceLang: translationResult.sourceLang,
         translationMeta: translationResult.translationMeta,
         availableTranslations: translationResult.availableTranslations,
         liked,

apps/core/src/processors/helper/helper.translation.service.ts

@@ -22,6 +22,7 @@ export interface TranslationResult {
   content?: string
   contentFormat?: string
   isTranslated: boolean
+  sourceLang?: string
   translationMeta?: TranslationMeta
   availableTranslations?: string[]
 }
@@ -69,15 +70,20 @@ export class TranslationService {
     const normalizedTarget = normalizeLanguageCode(targetLang)
 
     try {
-      const { availableTranslations, translation } =
+      const { availableTranslations, sourceLang, translation } =
         await this.aiTranslationService.getTranslationAndAvailableLanguages(
           articleId,
           normalizedTarget || undefined,
           allowHidden ? { ignoreVisibility: true } : undefined,
         )
 
       if (!normalizedTarget || !translation) {
-        return { ...originalData, isTranslated: false, availableTranslations }
+        return {
+          ...originalData,
+          isTranslated: false,
+          sourceLang: sourceLang ?? undefined,
+          availableTranslations,
+        }
       }
 
       return {
@@ -89,6 +95,7 @@ export class TranslationService {
         content: translation.content,
         contentFormat: translation.contentFormat,
         isTranslated: true,
+        sourceLang: translation.sourceLang,
         translationMeta: {
           sourceLang: translation.sourceLang,
           targetLang: translation.lang,

apps/core/test/src/processors/helper/helper.translation.service.spec.ts

@@ -145,6 +145,7 @@ describe('TranslationService', () => {
         summary: 'Translated Summary',
         tags: ['translated-tag'],
         isTranslated: true,
+        sourceLang: 'zh',
         translationMeta: {
           sourceLang: 'zh',
           targetLang: 'en',