Fallback to default language for empty strings

Use the default language strings for keys which have empty values
in the translation file. ( i.e. when the translation file is
incomplete )

Author: akshay-99

src/core/internationalization.js

@@ -36,6 +36,7 @@ export const initialize = () =>
         nestingPrefix: '$tr(',
         nestingSuffix: ')',
         defaultNS: 'translation',
+        returnEmptyString: false,
         interpolation: {
           escapeValue: false
         },