There is also a readily installable Flatpak:

https://github.com/sonnyp/Eloquent

It is restricted by Flatpak (i.e. Control Groups and Namespaces):

   * No file-system access
   * No access to devices
   * Network Access is allowed (API of Languagetool is only reachable via REST?)

It is fat. But that's more an issue of Java itself. I only wish Languagetool didn't use Java, which is fine on a servers but horrible on personal-computers. Implemented in C, C++ or Rust and it would be probably already part of LibreOffice. Sonny Piers is the packager Flatpak, a prominent ex-member of GNOME board. He was removed due some Code-Of-Conduct thing which nobody can explain, due to issues within the Code-Of-Conduct.

PS: LibreOffice had to fight years to remove Java which plagued the project.