This multilingual site is born around 3 years ago (WP 3.0). Since lot of improvements in WP Core and versions of xili-language plugin…
Example twentyten-xili is downloadable now in version 3.0 and uses recent technic (classes and more…). He is also compatible 3.5+. Technical infos are here on website showing twentythirteen-xili.
Here posts and how to are are left in place as learning.
So remember to read the date of the article and the versions !!