If you're a developer, have you considered contributing to LanguageTool? We have collected some easy tasks to get you started: https://github.com/languagetool-org/languagetool/issues?labels=easy+fix&state=open
Just fork us on github, fix an issue, and send a pull request. We're here to help you if you have any questions.
If you're not a developer: we're constantly looking for language maintainers. What does that mean? We've documented that at http://wiki.languagetool.org/tasks-for-language-maintainers