Sublanguage selector goes blank at SA @ X deployment

[RichDom2185]

Testing locally, we see that when a course does not enable a language, the language selector at the top right is still rendered. This leads to cases where selecting a language with no sublanguages enabled for the course results in the following empty dropdwon:

[RichDom2185]

This is because the sublanguage menu items are conditionally rendered using Constants.playgroundOnly. Will need to create a non-hacky fix.