feat(translation-store)): add subject to inform on fallback lang use

Author: HerrDerb

projects/ngx-translate/src/lib/translate.service.ts

@@ -65,6 +65,10 @@ export interface FallbackLangChangeEvent {
     translations: InterpolatableTranslationObject;
 }
 
+export interface FallbackLangUseEvent {
+    lang: string;
+    missingTranslationKey: string;
+}
 /** @deprecated use `FallbackLangChangeEvent` */
 export type DefaultLangChangeEvent = FallbackLangChangeEvent;
 

projects/ngx-translate/src/lib/translate.store.ts

@@ -2,6 +2,7 @@ import { Injectable } from "@angular/core";
 import { Observable, Subject } from "rxjs";
 import {
     FallbackLangChangeEvent,
+    FallbackLangUseEvent,
     InterpolatableTranslation,
     InterpolatableTranslationObject,
     LangChangeEvent,
@@ -21,6 +22,7 @@ export class TranslateStore {
     private _onLangChange: Subject<LangChangeEvent> = new Subject<LangChangeEvent>();
     private _onFallbackLangChange: Subject<FallbackLangChangeEvent> =
         new Subject<FallbackLangChangeEvent>();
+    private _onFallbackLangUse: Subject<FallbackLangUseEvent> = new Subject<FallbackLangUseEvent>();
 
     private fallbackLang: Language | null = null;
     private currentLang!: Language;
@@ -127,6 +129,10 @@ export class TranslateStore {
             this.fallbackLang != null &&
             this.fallbackLang !== this.currentLang
         ) {
+            this._onFallbackLangUse.next({
+                lang: this.currentLang,
+                missingTranslationKey: key,
+            });
             text = this.getValue(this.fallbackLang, key);
         }
         return text;