I don’t know where to report issues (is there a BugZilla somewhere?) so here is one:
on Ubuntu 16.04 and Libreoffice 5.4.4, with LanguageTool 4.0, every time I open a Writer document, a file LanguageTool.log is created in my home directory ($HOME).
Such log file should be created in a dedicated directory (in $HOME/.config/libreoffice, or in $HOME/.cache or in /tmp or somethink like) but not in the home directory.
With LanguageTool 3.0, there was no such issue.