MOBILE-2383 lang: Load parent lang if found

scripts/langindex.json

@@ -1412,6 +1412,7 @@
   "core.openinbrowser": "local_moodlemobileapp",
   "core.othergroups": "group",
   "core.pagea": "moodle",
+  "core.parentlanguage": "langconfig",
   "core.paymentinstant": "moodle",
   "core.percentagenumber": "local_moodlemobileapp",
   "core.phone": "moodle",

src/lang/en.json

@@ -174,6 +174,7 @@
     "openinbrowser": "Open in browser",
     "othergroups": "Other groups",
     "pagea": "Page {{$a}}",
+    "parentlanguage": "",
     "paymentinstant": "Use the button below to pay and be enrolled within minutes!",
     "percentagenumber": "{{$a}}%",
     "phone": "Phone",

src/providers/lang.ts

@@ -40,8 +40,7 @@ export class CoreLangProvider {
 
         platform.ready().then(() => {
             this.getCurrentLanguage().then((language) => {
-                translate.use(language);
+                this.changeCurrentLanguage(language);
-                moment.locale(language);
             });
         });
 
@@ -97,8 +96,31 @@ export class CoreLangProvider {
         // Change the language, resolving the promise when we receive the first value.
         promises.push(new Promise((resolve, reject): void => {
             const subscription = this.translate.use(language).subscribe((data) => {
+                // It's a language override, load the original one first.
+                const fallbackLang = this.translate.instant('core.parentlanguage');
+
+                if (fallbackLang != '' && fallbackLang != language) {
+                    const fallbackSubs = this.translate.use(fallbackLang).subscribe((fallbackData) => {
+                        data = Object.assign(fallbackData, data);
                         resolve(data);
 
+                        // Data received, unsubscribe. Use a timeout because we can receive a value immediately.
+                        setTimeout(() => {
+                            fallbackSubs.unsubscribe();
+                        });
+                    }, (error) => {
+                        // Resolve with the original language.
+                        resolve(data);
+
+                        // Error received, unsubscribe. Use a timeout because we can receive a value immediately.
+                        setTimeout(() => {
+                            fallbackSubs.unsubscribe();
+                        });
+                    });
+                } else {
+                    resolve(data);
+                }
+
                 // Data received, unsubscribe. Use a timeout because we can receive a value immediately.
                 setTimeout(() => {
                     subscription.unsubscribe();