improve locale setting

src/stores/i18n.js

@@ -1,6 +1,10 @@
 import Cookies from 'js-cookie'
+import messages from 'src/i18n/messages'
+import localeService from 'src/services/locale/locale.service.js'
 import { defineStore } from 'pinia'
 
+const BACKEND_LANGUAGE_COOKIE_NAME = 'userLanguage'
+
 export const useI18nStore = defineStore('i18n', {
   state: () => ({
     i18n: null,
@@ -11,5 +15,12 @@ export const useI18nStore = defineStore('i18n', {
         i18n: newI18n.global,
       })
     },
+    setLanguage(value) {
+      messages.setLanguage(this.i18n, value)
+      Cookies.set(
+        BACKEND_LANGUAGE_COOKIE_NAME,
+        localeService.internalToBackendLocaleMulti(value),
+      )
+    }
   },
 })