Hey, yeah sorry about that. There is little one can do about in JS-land. We tried to push the browser makers via the editing taskforce to give more direct access to the dictionaries to JS. Unfortunately, they seem to think this would be a security issue, because one might draw conclusions from custom entries in the dictionaries.
Say for example someone writes “Piotr is my neighbour”. Usually “Piotr” would be marked as incorrect, because it’s not part of the standard English dictionaries. But in the case of some user it’s not marked. The JS app can then conclude that the user must have added this word to the dictionary at some time. it could then send that information to the server and little by little profile the user. This would be even more true if the browser would give direct access to spelling suggestions.
I suggested the easiest would be to only give access to standard dictionaries without any custom entries, but apparently at least Safari isn’t technically able to do that. A suggestion from browser makers has been to allow the user to mark a range as needing correction.