Persist language settings using local storage

When user logs in, language setting will be stored in local storage.
Once stored, user does not have to re-select preferred language, but can
still update language settings on the login page.

Before a language is saved to local storage the locale = null
Renamed 'en.json' to 'en-US' because the vue i18n plugin defaults to
'en-US' when a language is not selected or null.
https://github.com/kazupon/vue-i18n/blob/v8.x/src/index.js#L67

Signed-off-by: Dixsie Wolmers <dixsie@ibm.com>
Change-Id: I577db3c4578eab30fbfae997dad0ece456fdf231
diff --git a/src/i18n.js b/src/i18n.js
index 09b3f4c..745d050 100644
--- a/src/i18n.js
+++ b/src/i18n.js
@@ -21,9 +21,12 @@
 }
 
 export default new VueI18n({
-  // default language is English
-  locale: 'en',
-  // locale messages with a message key that doesn't exist will fallback to English
-  fallbackLocale: 'en',
+  // Get default locale from local storage
+  locale: localStorage.getItem('storedLanguage'),
+  // Locales that don't exist will fallback to English
+  fallbackLocale: 'en-US',
+  // Falling back to fallbackLocale generates two console warnings
+  // Silent fallback suppresses console warnings when using fallback
+  silentFallbackWarn: true,
   messages: loadLocaleMessages()
 });