add i18n to frontend, still incomplete, but a start

lnbits/static/js/base.js

@@ -1,6 +1,14 @@
 /* globals crypto, moment, Vue, axios, Quasar, _ */
 
+Vue.use(VueI18n)
+
 window.LOCALE = 'en'
+window.i18n = new VueI18n({
+  locale: window.LOCALE,
+  fallbackLocale: window.LOCALE,
+  messages: window.localisation
+})
+
 window.EventHub = new Vue()
 window.LNbits = {
   api: {
@@ -320,6 +328,7 @@ window.LNbits = {
 }
 
 window.windowMixin = {
+  i18n: window.i18n,
   data: function () {
     return {
       g: {
@@ -335,6 +344,10 @@ window.windowMixin = {
   },
 
   methods: {
+    changeLanguage: function (newValue) {
+      window.i18n.locale = newValue
+      this.$q.localStorage.set('lnbits.lang', newValue)
+    },
     changeColor: function (newValue) {
       document.body.setAttribute('data-theme', newValue)
       this.$q.localStorage.set('lnbits.theme', newValue)
@@ -364,6 +377,12 @@ window.windowMixin = {
     }
     this.g.allowedThemes = window.allowedThemes ?? ['bitcoin']
 
+    let locale = this.$q.localStorage.getItem('lnbits.lang')
+    if (locale) {
+      window.LOCALE = locale
+      window.i18n.locale = locale
+    }
+
     addEventListener('offline', event => {
       this.g.offline = true
     })