YunoHost application is here: https://apps.yunohost.org/app/languagetool
Docs for installing LanguageTool manually are here: https://dev.languagetool.org/http-server - version 20260528 works on Debian 13 under WSL, needs openjdk-25-jre-headless and the --public option. The extension settings have a localhost option, I didn't have to change anything else.
Note that premium as of today costs $2.50 per month if you pay for two years in advance. Running LanguageTool on a laptop isn't very fast for languages other than English, so paying them for the cloud might provide a better experience than self-hosting.