feat: i18n support (#40)

ui/flutter/lib/widget/directory_selector.dart

@@ -26,12 +26,12 @@ class _DirectorySelectorState extends State<DirectorySelector> {
           readOnly: true,
           controller: widget.controller,
           decoration: widget.showLabel
-              ? const InputDecoration(
-                  labelText: "下载目录",
+              ? InputDecoration(
+                  labelText: 'setting.downloadDir'.tr,
                 )
               : null,
           validator: (v) {
-            return v!.trim().isNotEmpty ? null : "请选择下载目录";
+            return v!.trim().isNotEmpty ? null : 'setting.downloadDirValid'.tr;
           },
         )),
         IconButton(

ui/flutter/lib/widget/file_list_view.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:get/get.dart';
 import '../util/util.dart';
 
 import '../api/model/resource.dart';
@@ -29,7 +30,8 @@ class _FileListViewState extends State<FileListView> {
       crossAxisAlignment: CrossAxisAlignment.start,
       children: [
         const Padding(padding: EdgeInsets.only(top: 10)),
-        Text("选择文件", style: TextStyle(color: themeData.hintColor)),
+        Text('create.selectDir'.tr,
+            style: TextStyle(color: themeData.hintColor)),
         Expanded(
             child: Container(
                 margin: const EdgeInsets.only(top: 10),