From Meta, a Wikimedia project coordination wiki
Guidelines for Twitter, Facebook, and Google Plus Suggestions 
- Wikipedia fans on Facebook and Twitter are primarily readers, rather than editors. Posts should be of potentially broad interest, rather than targeted only to active editors and volunteers. However, there's room for community announcements and events, but we should be sensitive to our audiences.
- Suggested posts should be concise, and generally should not include more than one link.
- Remember, our social handles are also about conversations, not just one-way broadcast pushes, so if you spot online conversations that we should be part of, please point them out.
- If you speak multiple languages, please provide posts in English and any other languages you would like. Wikipedia is in 285 languages, so our posts should reflect that!