TT#132150 Fix language selection if default browser language is not en-US

Steps to reproduce:
* open broser settings and set any language which is not supported by CSC yet. You can chech that it was applied by executing "navigator.language" in the browser console.
* clean session storage for the CSC
* refresh the page.

** result before the fix: language selector are not displayed
** Expected result: language selector is present and language set to Englist (because it is defined as default language in CSC)

Change-Id: I2d53e649e14e3d82e2a5c1be4f99168971cd258c

src/boot/i18n.js

@@ -2,7 +2,9 @@
 import Vue from 'vue'
 import VueI18n from 'vue-i18n'
 import {
-    messages
+    messages,
+    getLangFromBrowserDefaults,
+    normalizeLocaleCode
 } from 'src/i18n'
 import {
     hasSession,
@@ -25,9 +27,9 @@ export default ({ app, store }) => {
     app.i18n = i18n
     store.$i18n = i18n
     if (!hasSession('locale')) {
-        setSession('locale', navigator.language)
+        setSession('locale', getLangFromBrowserDefaults())
     }
-    i18n.locale = getSession('locale') + ''
+    i18n.locale = normalizeLocaleCode(getSession('locale'))
 
     store.watch(() => i18n.locale, () => {
         store.dispatch('reloadLanguageRelatedData')

src/i18n/index.js

@@ -63,9 +63,10 @@ export function setLanguage (lang) {
     setSession('locale', lang)
     i18n.locale = lang
 
+    const quasarLangCode = lang.toLowerCase()
     import(
         /* webpackInclude: /(en-us|de|es|fr|it|ru)\.js$/ */
-        'quasar/lang/' + lang.toLowerCase()
+        'quasar/lang/' + quasarLangCode
     ).then(lang => {
         Quasar.lang.set(lang.default)
     })
@@ -94,3 +95,15 @@ export function convertLangV1toV2 (lang) {
 export function getCurrentLangAsV1Format () {
     return convertLangV2toV1(i18n.locale)
 }
+
+export function normalizeLocaleCode (locale) {
+    const shortLangCode = String(locale || defaultLocale).substr(0, 2).toLowerCase()
+    const langCodeInV2Format = (shortLangCode === 'en') ? 'en-US' : shortLangCode
+    const langCode = Object.keys(messages).filter(l => l === langCodeInV2Format)[0]
+    return langCode || defaultLocale
+}
+
+export function getLangFromBrowserDefaults () {
+    const browserLanguage = navigator?.language
+    return normalizeLocaleCode(browserLanguage)
+}