I haven’t had that happen to me yet, but it sounds annoying as hell. The “undetermined” language shouldn’t exist. That needs be a silent default. The user should be able select their primary language with a drop-down menu. The combo box would still exist but it’d be completely optional.

In your case it’d be nice if the “Select Language” drop-down was automatically set to the community’s default language. And maybe put a little red icon next to it when your language settings are incompatible.