Feature freeze for LanguageTool 5.4

Just a quick reminder that we’re now in feature freeze for LanguageTool 5.4, to be released 2021-06-25 (Release Roadmap | dev.languagetool.org ). Please don’t introduce new strings in the UI that require translation, and don’t introduce new features or larger code changes. Adding new rules is okay, as long as they are properly tested.