WordPress.org

Where can I see websites using this plugin ?

dev.xiligroup.com here and www.xiliphone.mobi here also usable with mobile as iPhone.

And as you can see in stats, hundreds of sites use xili-language.

For commercial websites, is it possible to buy support ?

Yes, use contact form here.

Support Forum or contact form ?

Effectively, prefer forum to obtain some support.

Does xiligroup provide free themes ?

No yet, but a lot of well designed themes like fusion or Arclite are very easily adaptable ( or the author incorporates automatic detection of xili-language as presented here ). And xili-dictionary avoids to use poEdit to update .mo files with contents of terms of your database (categories, ...)