Confirm the target input source first

Open System Settings → Keyboard → Text Input → Edit and confirm the source is in the enabled list. Select it once from the macOS input menu and type in a normal text field. If it cannot type before locking, fix the input method installation first.

Enable input source locking

  1. Open Input Method Manager.
  2. Select the enabled source you want to keep.
  3. Turn on “Lock current input source.”
  4. Leave the app running and switch to another app.
Input Method Manager menu bar control for locking the current input source
The lock can be controlled from the app and its menu bar menu.

What the lock does and does not do

While the app runs, it watches the active macOS input source and restores the selected one when needed. Enabling the lock stops automatic per-app switching so the two modes do not compete. Quitting the app stops this automation.

The menu name did not change?

If only a Chinese/English mode changed inside Squirrel or another input method, review that input method’s own key bindings. The lock manages macOS input sources.

Verify before relying on the rule

  1. Switch between two apps three times.
  2. Manually choose another input source and confirm the selected source returns.
  3. Quit Input Method Manager and confirm automatic restoration stops; reopen it to resume.

If the lock cannot restore the source, check that it remains enabled in macOS and that Input Method Manager has the permissions shown in its authorization card.