Language Override not working

I'm using the language over ride to change things like VAT to Sales Tax, but my email formats are not changing them.

On joomla 1.7, language overrides don't work for some emails because of the changes put in place by joomla in the language handling library.
You'll have to either put the changes directly in your translation file (don't forget to back it up before updating HikaShop) or edit your emails via the menu System->Emails (Business edition only) and replace the string directly there.

Any chance this will be remedied in a future version of Hikashop?

As is, the override field only serves a a backup for strings that have to be changed in the main languagefile, so it's not really an override field (at least not in Joomla 1.7)

We have found a way to do it differently in order to avoid the problem.
We'll look at adding that in the future yes.

Great!