In addition to https://github.com/geany/geany/pull/3171 I'd like to merge this PR too so there's a proper lexer for the Nim language. I just went through the PR and tested it a bit and all seems to work well.
Again, I'll wait for about a week for complaints and merge this afterwards.
(Misusing hot summer days where nobody pays attention to get some old patches of mine merged :-P.)