@PolyMeilex would you be interested in a PR for localization? I looked a little bit in the code and I see few other places where strings are hardcoded:

• rfd/src/backend/linux/zenity.rs

  Line 192 in 81e0dd3

  command.args(["--ok-label", "Ok"]);

• rfd/src/backend/macos/message_dialog.rs

  Line 43 in 81e0dd3

  MessageButtons::Ok => vec!["OK".to_owned()],

• rfd/src/backend/wasm.rs

  Line 109 in 81e0dd3

  btn.set_inner_text("Ok");

• rfd/src/message_dialog.rs

  Line 199 in 81e0dd3

  Self::Yes => "Yes".to_string(),

• rfd/src/backend/gtk3/message_dialog.rs

  Line 36 in 81e0dd3

  Some((CString::new("Yes").unwrap(), gtk_sys::GTK_RESPONSE_YES)),

• rfd/src/backend/macos/message_dialog.rs

  Line 43 in 81e0dd3

  MessageButtons::Ok => vec!["OK".to_owned()],

• rfd/src/backend/macos/utils/user_alert.rs

  Line 45 in 81e0dd3

  MessageButtons::OkCancel => [None, Some("Cancel".to_string()), None],

I see there is the crate rust-i18n that looks promising.
I think the difficulty is "how to find the current locale for each backend". -> oh I just found out there is sys-locale
Let me know if you are interested, I will be happy to use my spare time to help.

I would rather not introduce more dependencies and complexity.

• On Windows everything works out of the box already.
• On Zenity backend, I would like to use the localization support Zenity already has internally, it just sadly seems to not be exposed to the users atm, even tho needed localization strings are already there.
• And on MacOS I have no idea, there is probably no build-in localization string for this.

The *Custom labels are supported, so users can always do the localization manually.