Add Simplified Chinese (zh-CN) localization to the desktop app

What problem are you trying to solve?

I work primarily in Chinese. The assistant responds in Chinese without any
issue, but the desktop interface is English-only — there is no option to
change the interface language anywhere in Settings. So every navigation
label, settings page, button, dialog, and system message has to be read in
a second language, which adds constant low-level friction to everyday use.

What would improve it?

Simplified Chinese localization for the desktop app — at minimum the
surfaces I see most often: navigation, Settings, buttons, dialogs, and
system messages.

A language option in Settings (System default / English / 简体中文) would
be a good starting point. Even a partial translation of the most frequently
seen screens would be a meaningful improvement. Ideally the CLI would
follow, but the desktop is where it matters most for me.

I understand full localization is a large undertaking, so I'm not expecting
complete coverage immediately.

What do you do today?

Read all interface text in English. I've gotten used to the common labels,
but unfamiliar or newly added screens still take extra effort to parse.

Product area

None

首先定位桌面应用 Settings 中的语言控件，以及用于导航、按钮、对话框和系统消息的代码或资源。定义 Simplified Chinese 的初始范围，以及该选项如何与 System default 和 English 并列显示。完成的标准是：所选语言会更改已约定的桌面界面，并清楚记录部分覆盖范围。