Hell of a vote for this one!
But unfortunately, this isn't really a "bug". It works as intended. When you change the UI language, it sets a variable in a cookie in your browser local storage. Unlike the rest of the fields, it does not broadcast your language preference to the blockchain; therefore, the "update" button has no use of being enabled after changing the language.
Maybe a feature request to suggest putting the language on the blockchain would be fitting, but I am reluctant to code this as a bug. Perhaps if I get some free time later.
Oh okay, then there should be a notification or something, it's really not intuitive that way
EDIT: I just realized that the language changes automatically when I switch it in the options, I don't think that was the case at the time I posted this, or maybe am I just blind ^^