Multilingual child theme of Twenty Eleven bundled (embedded) theme of WordPress : TwentyEleven-xili v. 1.8.1
Master Branch is reserved for latest version of xili-language 2.15.0+
This example is visible (and documented) here
After installation or updating, it is fully recommanded to refresh permalinks.
-- a child theme needs his parent theme named twenty eleven v. 1.8 --
IMPORTANT: Before updating don't forgot to keep a backup of the current languages files (.mo, .po) in child sub-folder.