need help which version should i install

Hello,
I am currently using the 3.2.1 version. I use wmpl for the translations.
I tried to install the last 3.5.1 version but it breaks everything (the 2 languages appear on the same page)
So I went back to my old version
Now I need new plugins running with more recent versions.
Who could help me? Which more recent version could I install without loosing my translation features?

Thanks very much for help
Best