Hi mattyoaks,
Change the display language
The display language is the language that Windows uses in wizards, dialog boxes, menus, and other items in the user interface. Some display languages are installed by
default, and others require you to install additional language files.
Click the Keyboards and Languages tab. ( found in control panel) - Under Display language, choose a language from the list, and then click OK.
Note- If you don't see the list of display languages, you need to install additional language files first. For more information, see Install a display language.
This was copied and pasted from 'Help and Support'. You'll have to also change keyboard input and so on. All this can be found via the control panel and 'clock,region and language'.