In the test project attached, I create a simple MainWindow that has an "About" action, a "File/Open" action, a "Help/Change Language" action, and a dialog button box only as a visual element to check that the language changed. The demo starts in English and has all the actions visible.

To reproduce the bug:

• Run the demo.
• Change the language via the action (or hit CMD+L). The dialog button box will change language, but the actions won't cause they haven't refreshed yet.
• Do a simple app switch (CMD+TAB) and return to the demo in order to refresh the menu actions
• The "ActionTest" menu should be translated by now, and the File/Open action should be hidden/removed.

If I remove or change the qtbase_cs.ts translation of "QCocoaMenuItem/About" the problem is fixed.

My guess is that the Czech translation of "About", that is a simple "O", somehow confuses the macOS system to hide the File/Open action.