Please carefully follow the instructions in the ReadMe.txt file as it contains VERY important informations.
If you are upgrading from XOOPS 2.0.10 with XOOPS Multilanguages 2.0, you can follow the instructions of XOOPS_2.0.13_ML_2.0.2/ReadMe.txt in order to upgrade to XOOPS 2.0.13 and XOOPS Multilanguages 2.0.2 in 1 step.