Word - language - UK/US English

Tedraker 

Have you been able to change the display language in Windows? Have you also managed to correctly set the proofing language in Word's Language dialog box (Review > Language > Set Proofing Language)? Try creating a new, blank document in Word by pressing Ctrl+N. If the language is correct in that document, your steps have been successful. 

Note that existing documents won't be affected after you have changed the defaults; instead, these must be dealt with one by one. For example, you can modify the language of the Normal style in each document. Often, though, you have to select all the text and manually (re-)apply the correct language via Review > Language > Set Proofing Language (just click OK, and do not click the Set As Default button, since you are not changing the defaults in this instance).