feat: support more langs

* add translations for French, Spanish, and Italian
* change the wording for better understanding of this feature:
    - "import" to "restore"
    - "export" to "backup"
* rename functions to reflect these changes

src/www/js/api.js

@@ -138,19 +138,12 @@ class API {
     });
   }
 
-  async uploadConfiguration(file) {
+  async restoreConfiguration(file) {
     return this.call({
       method: 'put',
-      path: '/wireguard/upload',
+      path: '/wireguard/restore',
       body: { file },
     });
   }
 
-  async downloadConfiguration() {
-    return this.call({
-      method: 'get',
-      path: '/wireguard/dl',
-    });
-  }
-
 }