Good points! Good to finally have languages as structured data. Few confirmations and suggestions:
- Do distinguish between reading and writing skills as suggested.
- So as not to reinvent the wheel and be compatible with the rest of the world, use the CEFR codes for skill levels. Old Babel system codes can be mapped.
- Allow users to specify their languages even when not in predefined lists. There are thousands of languages and variants not yet in current directories of languages. We should not miss them.