Set userLanguage cookie when setting interface language

src/components/settings_modal/tabs/general_tab.js

@@ -72,6 +72,12 @@ const GeneralTab = {
         !this.$store.state.users.currentUser.background_image
     },
     instanceShoutboxPresent () { return this.$store.state.instance.shoutAvailable },
+    language: {
+      get: function () { return this.$store.getters.mergedConfig.interfaceLanguage },
+      set: function (val) {
+        this.$store.dispatch('setOption', { name: 'interfaceLanguage', value: val })
+      }
+    },
     ...SharedComputedObject()
   },
   methods: {