Add language/locale configuration option

[meesu9]

Title: Add language/locale configuration option

Category: Feature Requests, Ideas

Body:

Summary

It would be very useful to have a configuration option to set the language/locale directly in Ghostty's config file, rather than relying solely on system environment variables.

Motivation

Currently, Ghostty's language can only be changed by:

1. Modifying system locale settings (macOS: System Settings → Language & Region)
2. Setting environment variables (LANG, LC_ALL) before launching

This is inconvenient for users who want to:

• Use Ghostty in a different language than their system
• Switch between languages frequently without changing system settings
• Have per-instance language control

Proposed Solution

Add a configuration option such as:

Set the language for Ghostty UI

language = zh_CN.UTF-8

Or alternatively:

Set the locale for translations

locale = zh_CN

This would allow users to easily set their preferred language in the config file at:

• macOS: ~/Library/Application Support/com.mitchellh.ghostty/config
• Linux: ~/.config/ghostty/config

Implementation Considerations

• The config option should override system locale if set
• Should support hot-reload if possible (like other config options)
• Fallback to system locale if not specified or invalid
• Should validate against available locales in src/os/i18n_locales.zig

Alternatives

The current workaround is to use an alias or wrapper script, but this is less discoverable and less integrated with Ghostty's configuration system.

[pluiedev]

This is something that has been asked before so I'll accept it. The way to hot-reload languages for gettext/libintl is very cursed, but we can definitely make it work.

[pluiedev]

#10276