There are several issue with this code:
- it still uses kchmshell4, so it's broken anyway;
- even if changed to kcmshell5, the 'languages' modules does not exist anymore;
- there are few alternatives, but in general the language settings used by Qt5 follows the settings in the system, nothing "KDE specific";
- it is possible to change the language from the Help menu.
So it's better to completely remove this action.