The language needs to be set at the time of installation. With the trial, you only get one chance to do that.
Now, you say that you entered the S/N. Did you purchase the full-paid version? Do you still have the download file from the Adobe site, if you did purchase? If you did buy, and have the downloaded installation file, you can Uninstall, then re-Install, choosing the language of the program's interface.
Do NOT unInstall, if you still have the trial, as you will NOT be able to re-Install.
Also, there have been reports of some issues, where one had the OS set to one language, the keyboard set to maybe another, and then some Adobe programs set to yet another. I have not heard of language issues with PrE, but both PS and PrPro have had some quirks.
I installed the trial, tried PrE for awhile, then purchased a full-paid version and entered the S/N on the retail CD in the trial to activate it.
I still have the install of the demo I downloaded and also have the install on the CD I purchased.
is it safe to uninstall/reinstall ? do I need to deactivate PrE before uninstalling ?
Especially with that installation DVD and your S/N, there should be no issues whatsoever. If you have any doubts, you might want to do a system backup. Also, doing a System Restore Point before you do any uninstall/reinstall is a good thing also.
It's very simple . You have to uninstall and then re-install in English as language.