If it is happening to some threads in specific, it's likely a result of that little database-encoding accident that happened. It affects among other things és, long hyphens, typographical (curved) quote symbols (produced when pasting from word processors) and a few other glyphs.
It is possible to manually correct them if you find this happening to your posts, otherwise if it's a breaking thing the best thing to do is to notify the section mod I think?
If this is happening at large, you might have hit a cnfiguration issue in your browser and it's reading the wrong "web language" I guess, but I wouldn't know what else to say about it.