The first thing to keep in mind is that you need enough experience in translation and/or interpretation before you apply.
The procedure varies from country to country. You can either pass a specific exam, or just apply directly to the administration. Usually it takes some time to take your application into consideration (in France it can take up to a year) before you get an answer.
Another example: Once you become a Sworn Translator in Spain, you receive a card that specifically says you are a sworn translator allowed to translated in specific languages.