MenuItem mnemonic should be a property that is not dependent on parsing the MenuItem text. If the mnemonic character is not part of the main text the displayed text should be amended with the mnemonic. Often translations to other languages leave the Mnemonic independent of the main menu item text. E.g. Chinese "Save" menu item will still use S as the mnemonic. Swing's JMenuItem supports this so developers migrating to JavaFX from Swing may expect it.