feat(i18n): 添加多语言支持功能

- 新增国际化系统，支持中英文切换
- 添加语言选择对话框和语言切换按钮回调
- 扩展配置系统以支持语言设置存储
- 创建语言文件目录结构和占位文件
- 更新主窗口支持UI文本动态刷新

libs/gettext/license.txt

@@ -0,0 +1,30 @@
+MIT License
+
+Copyright (c) 2013-2026 Michele Locati
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+This project includes the following third-party components:
+
+- iconv ( https://www.gnu.org/software/libiconv/ )
+  See license in the file licenses/iconv.txt
+- gettext ( https://www.gnu.org/software/gettext/ )
+  See license in the file licenses/gettext.txt
+- The GCC ( https://gcc.gnu.org/ ) runtime libraries provided by mingw-w64
+  See license in the file licenses/gcc.txt