I got annoyed by seeing lots of ? instead of some characters so I decided to try to "guess" encoding. I changed it first to latin2, then latin4 and utf-7 (all done inside settings->reading). Last change made me unable to save eny changes to settings giving me
Your attempt to edit your settings has failed.
it has also disabled Visual editor (but it still has check flag in settings), makes similar error when saving/publishing post and gives blank page after submiting comments.
I realy don't know what to do, didn't mess around with anything because I didn't want to make even bigger mess. Some tutorials and answers I found only give temp solution or fix one of the issues I have.