Question Maybe stupid questions

Sorry for the following questions, but work is getting me crazy these days...

1) I'm obviously using a Custom ROM with italian language and would like to install:
is it sufficient I change my ROM language?
2) Since it is a OS update, I don't need to backup my application data stored in
their IsolatedStorage directories, because I won't lose any saved data... It is
only a matter of OS files updating, am I right? (even if my english is decent, my
neuron is driving me towards the bed... )