added LocaleSaver.vue

src/App.vue

@@ -3,12 +3,14 @@ import {RouterView} from 'vue-router';
 import {Options, Vue} from 'vue-class-component';
 import DocumentLocaleSetter from '@/components/locale/DocumentLocaleSetter.vue';
 import NavBar from '@/components/NavBar.vue';
+import LocaleSaver from '@/components/locale/LocaleSaver.vue';
 
 @Options({
   name: 'App',
   components: {
     NavBar,
     DocumentLocaleSetter,
+    LocaleSaver,
     RouterView,
   },
 })
@@ -19,6 +21,7 @@ export default class App extends Vue {
 
 <template>
   <div class="d-flex flex-column h-100 w-100">
+    <LocaleSaver/>
     <DocumentLocaleSetter/>
     <NavBar/>
     <RouterView class="flex-grow-1"/>

src/components/locale/LocaleSaver.vue

@@ -0,0 +1,21 @@
+<script lang="ts">
+import {Options, Vue} from 'vue-class-component';
+import {Watch} from 'vue-property-decorator';
+
+@Options({name: 'LocaleSaver'})
+export default class LocaleSaver extends Vue {
+  mounted(): void {
+    const locale = window.localStorage.getItem('locale');
+    if (locale)
+      this.$i18n.locale = locale;
+  }
+
+  @Watch('$i18n.locale')
+  onLocaleChanged(value: string): void {
+    window.localStorage.setItem('locale', value);
+  }
+}
+</script>
+
+<template>
+</template>