TOTAL with VAT in status email

I have overridden the language string
TOTAL_WITH_VAT="TOTAL with VAT : %s"

to show as

TOTAL_WITH_VAT="TOTAL with GST : %s"

but on the order status notification email it still says TOTAL with VAT.

I think it is this line:

$text=JText::sprintf('TOTAL_WITH_VAT',$currencyHelper->format($data->cart->full_total->prices[0]->price_value_with_tax,$data->order_currency_id));

is there a bug?

Language overrides don't work on emails. So either you modify directly the email and change 'TOTAL_WITH_VAT' by "TOTAL with GST : %s" or you modify the original translation file.

If you actually use the en-US language file, the "VAT" is replaced by "tax" in the language file.