To foster engagement, bilingual content would be a great start (Post in non-English languages and offer English translations if capable) I know that many would be able to do that. This would not be too difficult for SN to incorporate, I'm sure. But would only make sense if there's a growing use of other languages.

Each post has a checkbox [ provide alternative language [ ] ] and... [ use as primary language [ ] ]

Not a totally easy thing to implement but it would definitely afford more space for SN to reach a wider readership. What's to lose?