Fix for #2787-Cannot watch video on develop branch.

Hi @aronasorman - this fixes #2787.

Branch **develop**

We made sure that the `lang_code` or `selected_language` variables have a value except `None`.

I have no idea where those variables are being used on the client-side but watching video on English or other language now works.

Just a note: I think we have introduced this bug while fixing #2717.