Never mind, I upgraded the smartlanguage module to the latest and works fine now.

Did you consider previous replies in this topic? I am strongly advise you to use EMLH instead of other derivations. With EMLH you are free from maintenance works. EMLH is only one multi-language hack that is friendly to caching system (which speeds up your site) (to be exact, only cubeUtils for XOOPS Cube can compete with EMLH)

1) Download and unzip EMLH
2) Put the php file under XOOPS_ROOT_PATH/include
3) Add one line to your mainfile.php

Your site is multilingual from now....