Unfortunately, the current ngrams for language tool cannot be read with lucene 8.5. The indexes have to be rebuilt for 8.5 (you cannot update the current ngrams beyond version 6). I communicated with the developer on this. Also version 4.9 has a bug, so use version 5.0 when updating. Currently, I went back to lucene 6.6 on leap 15.1 and manually installed it, and it does work with upgraded ngrams (you have to update them using lucene 5.5.5 upgrader tool to lucene 6 and it then works).

Any progress on this?