There really isn't a lot of multi-country advertising in Europe. You're going to run into bigger problems than showing correct VAT rates - language being probab

There really isn't a lot of multi-country advertising in Europe. You're going to run into bigger problems than showing correct VAT rates - language being probably the most obvious one, but also different regulatory requirements for things like mandatory warnings, watershed rules, etc. In practice, advertising is always going to need to be adapted for every European market.