Win11: Installed spellers are not working

[snomos]

Spellers for languages not served by MS (ie languages needing registration by kbdi) are installed by DM (FIT/Meänkieli in this case):

But they do not work, in the sense that when switching to the corresponding keyboard, the speller is not activated. In Word, this leads to the following message:

Word clearly indicates that there is no speller for the language, although the language itself is recognised, and the correct keyboard is activated.

There is also no trace of the new language (Meänkieli) in LibreOffice:

This used to work on Win10.

[snomos]

Things are working correctly for OEM languages:

Also in LibreOffice: