See #1038

All post meta data for the video_language field has been copied to the new language field so we can now remove video_language.

Areas affected

1. Column displaying video_language removed from admin table
2. Filter on admin table switched from video_language to language
3. Metabox field for video_language on edit screen removed (and saving of field)
4. Frontend filtering switched from video_language to language
5. Language on frontend single Tutorial details switched from video_language to language
6. Custom query to prioritize content in the user's locale switched from video_language to language
7. Tutorial application form schema switched from video_language to language
8. The video_language field is no longer registered

How to test

1. Before switching to this branch (ie. on trunk), ensure that some tutorials in your local instance have both video_language and language meta set (either set a few manually, or trash existing/destroy env and re-import from prod). These should have columns for 'Language' and 'Video Language' displayed in the admin table with matching values. When editing the Language field is the topmost document setting, and the video language is in the Workshop Details meta box:
   

2. Switch to this branch and check all of the above affected areas

3. For 7, try changing locale when viewing the tutorials page on the frontend, and observe any tutorials with language matching your locale being displayed first