The original version of your terms and conditions should be in the language of the country where your company is located or in your customer's language. As long as the terms and conditions are not an employment contract, you and your customers are free to chose the language you think suits you best, but your customers must first agree to sign terms and conditions in other language than yours or theirs.
In B2C relations within the EU you most likely should refer to laws of the country where your company is incorporated. You must comply with the local VAT rules and data protection acts. You should contact your local information commissioner and check whether you have to register any of your databases.
If you sell services outside the EU, you should register for VAT in each of the countries you sell the services in.