My keyboard layout is UK, so I must keep the UK layout. How can I change the system language (including dictionaries in browsers, libreoffice, etc) to US English?

I tried to change it from Language support, but English (US) is not active to be selected.

[![enter image description here](https://i.stack.imgur.com/DRVK5.png)](https://i.stack.imgur.com/DRVK5.png)