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/share/aclocal/nls.m4

@@ -0,0 +1,31 @@
+# nls.m4
+# serial 7 (gettext-1.0)
+dnl Copyright (C) 1995-2026 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+dnl
+dnl This file can be used in projects which are not available under
+dnl the GNU General Public License or the GNU Lesser General Public
+dnl License but which still want to provide support for the GNU gettext
+dnl functionality.
+dnl Please note that the actual code of the GNU gettext library is covered
+dnl by the GNU Lesser General Public License, and the rest of the GNU
+dnl gettext package is covered by the GNU General Public License.
+dnl They are *not* in the public domain.
+
+dnl From Ulrich Drepper, Bruno Haible.
+
+AC_PREREQ([2.50])
+
+AC_DEFUN([AM_NLS],
+[
+  AC_MSG_CHECKING([whether NLS is requested])
+  dnl Default is enabled NLS
+  AC_ARG_ENABLE([nls],
+    [  --disable-nls           do not use Native Language Support],
+    USE_NLS=$enableval, USE_NLS=yes)
+  AC_MSG_RESULT([$USE_NLS])
+  AC_SUBST([USE_NLS])
+])