Latchkey

A tiny native macOS background utility. Every time you switch to another app, Latchkey forces the system keyboard input source back to the one you picked. Choose your default layout once and you’ll always start typing in the right one.

• No Accessibility permission needed: it uses Text Input Sources (TISSelectInputSource) and listens for app-activation notifications.
• The picker lists only the input sources currently enabled in the system.
• Launch at login via SMAppService.
• Accessory app: no Dock icon, no menu bar (LSUIElement), single instance.
• First launch shows the window so you can configure it; login launches stay hidden.
• Pure AppKit + SwiftUI, no third-party dependencies.

How it works. Open Latchkey once, pick your preferred layout, and let it run in the background. From then on, whenever you activate another app, it resets the keyboard input source on its own, and you stop starting sentences in the wrong language.

Requires macOS 13+.