Show VAT instead of Taxes in checkout

I did find a post on how to do this and I can't find it again. In it, it said to change Taxes to VAT in the Language file. I have changed the default language file mp-default.po on line 1048 Taxes to VAT. However it still says Taxes in the checkout (I have cleared browser cache). Is there another file somewhere I have to change?

Many thanks
Paul