diff --git a/src/providers/lang.ts b/src/providers/lang.ts
index 266421412..04f8283ee 100644
--- a/src/providers/lang.ts
+++ b/src/providers/lang.ts
@@ -58,7 +58,7 @@ export class CoreLangProvider {
      * @param {string} [prefix] A prefix to add to all keys.
      */
     addSitePluginsStrings(lang: string, strings: any, prefix?: string): void {
-        lang = lang.replace('_', '-'); // Use the app format instead of Moodle format.
+        lang = lang.replace(/_/g, '-'); // Use the app format instead of Moodle format.
 
         // Initialize structure if it doesn't exist.
         if (!this.sitePluginsStrings[lang]) {
@@ -307,7 +307,7 @@ export class CoreLangProvider {
                 return;
             }
 
-            lang = values[2].replace('_', '-'); // Use the app format instead of Moodle format.
+            lang = values[2].replace(/_/g, '-'); // Use the app format instead of Moodle format.
 
             if (!this.customStrings[lang]) {
                 this.customStrings[lang] = {};
@@ -363,7 +363,7 @@ export class CoreLangProvider {
      * @param {string} value String value.
      */
     loadString(langObject: any, lang: string, key: string, value: string): void {
-        lang = lang.replace('_', '-'); // Use the app format instead of Moodle format.
+        lang = lang.replace(/_/g, '-'); // Use the app format instead of Moodle format.
 
         if (this.translate.translations[lang]) {
             // The language is loaded.