Usage of i18n and multi-site?
As i understood you almost cant use common tables on multi-site installation - i`ve been checking them one by one. First i configured all of sites - only the main site (from which tables were shared) could switch languages and translate nodes. On the others there were no switcher showing and translated nodes were not linking.

Maybe you can some, but still you got to have everything identical (starting from content types and endind with nodes)

Maybe i am wrong.