You are right and at the same time you are wrong. The mnemonic keys (thats the right term) work, but not as expected by you.
Microsoft published guidelines like Guidelines for Keyboard User Interface Design
and Mnemonics Guidelines
which in my experience are really great, but which most GUI programmers and GUI translators have never read. So it is not really surprising that the same mistakes are made again and again regarding mnemonic key assignment in menus, popup menus and dialogs.
I'm using nearly exclusively English UltraEdit and suggested in the pasted quite often improvements on mnemonic key assignment during beta test periods as also the developers and testers of IDM often forget to check the mnemonic keys and the tab sequence after a change in a menu or a dialog.
By luck I have currently installed also German beta version of next UE and could therefore look on German Find and Replace dialog.
As it can be seen on image above, some letters are used more than once, a mistake made by the German translators.
So on pressing W (no edit field as input focus) or Alt+W (necessary on edit field have input focus) just the input focus switches to either Ausgewählter Text
or Nur ganzes Wort vergleichen
. But the radio option is not automatically selected respectively the check box is not automatically toggled because another (enabled) resource in same dialog has the same mnemonic key assignment. So the user has to additionally press the SPACE key to select the radio option respectively toggle the check box.
Which item has the input focus is displayed with Classic theme with a black broken line rectangle around the item. But on using a modern and stylish theme like Slate there is no such visual help anymore to see which item has the input focus. I don't know if this is the fault of developers of UltraEdit or developers of GDIPlus library used by UltraEdit. However, it looks like stylish user interfaces are designed for being used by pointing devices or touch screens and not by keyboard. If a user only clicks or touches an item, it is not necessary to indicate which item has input focus like needed when the keyboard is used.
I will look on all 6 German find and replaces dialogs (4 tabbed plus the 2 in hex edit mode) and send a suggestion to IDM support by email to get in next major German version as most find/replace items not only accessible but also activated by key without duplicate assignments and with same mnemonic key for same option in all 6 dialog windows.