Change the whole computer language

Hello, Am Fabian
You did not mention which operating system. in any case, you need to backup you file(copy out our personal file) and reinstall the operating system. there are two ways you can do this;
1. running a system recovery if your system has a recovery partition or a recovery CDs/DVDs. then during the recovery process select the language you want and proceed.
2. if you don't have the operating system installation CD/DVD, buy from any software vendor near you, then use the CD/DVD to reinstall the operating system during which you then select the language you want.

note that the steps for installation is operating system dependent. you can find the steps for installing the operating system from the web site of its manufacturer its usually simple to follow.

i hope this information will be helpful.
Thanks