Yes, the slash character unfortunately broke for some folks with 2.0.5; you can use 2.0.4 for the time being until I get a fix out.
With Linux machines (English locale, querty keyboard), there was an issue where using the "comment lines" action (ctrl+/ by default) would fire both the comment-lines action, as well as the default "insert a / character" action. This looks to be because of a difference between Linux and Windows/OS X as far as keyTyped vs. keyPressed key events, and what is used to actually insert a "/" character when typing.
The fix that was put into 2.0.5 for this was to edit RsyntaxTextAreaDefaultInputMap to change the KeyStrokes for the slash-related actions, to force them to be identical across all OSes, and also to make them work
across all OSes (Windows, Linux, OS X, even tested Solaris). Unfortunately, this was all done on English locale, querty system setups. I evidently broke folks in other environments by doing this.
Once I can determine a way to get these actions working everywhere, I plan on creating a 18.104.22.168 release that has just this keyboard fix. If you have access to qwerty systems as well, and have the time/motivation, feel free to look into it
You can look at the 2.0.4 tag for RSyntaxTextAreaDefaultInputMap.java if you want to see the older, working, version. A diff of the changes is here
Sorry about the breakage!