For those who are struggling with regular expressions: I use this on an almost daily basis and it has never failed me.
That is a fantastic resource indeed!
I have been using this for years: http://www.regular-expressions.info/
It has an excellent reference page for many languages: http://www.regular-expressions.info/reference.html
Thank you for sharing, @Jan_Schreiber.
This link will help all newcomers, so maybe, adding it to the http://wiki.languagetool.org/development-overview would be fitted, even though it qualifies as advertisement.
Hopefully, it will attract people to develop unmaintained languages.