Determining where your visitors are physically located (geolocation) is possible but not 100% reliable. And whether you charge tax or not depends on where you ship the goods which not necessarily may be the same as the ip location of the customer. So, all very confusing for the customer.

Making this language-dependant would be even more confusing. I have a spanish/english site in spain, national and international customers use both languages.

I decided to make it clear the prices are with tax...this is removed when a customer is logged in with a tax-exempt address.