If you reinstall x5, you get to choose severel languages during install.

Your projects will be kept, but a backup of your project can never hurt.

Download top right next to your name pulldown -> download, full version and install that one.

There are almost 20 languages to choose from.

Hi Peter, 

I confirm that you can choose the installation language when installing the software and that you can change the language of the website from the Language Content Management window. Please consider that this will change the buttons languages, but obviously you will have to translate the texts you have inserted yourself. 

Thank you! Have a nice day.