It is important to realise that having a knowledge of two languages does not necessarily mean one will be a good translator. Theoretical knowledge on its own is also not enough. One has to have a natural ability for transferring the underlying meaning and nuances, which many people are not able to do successfully. Practice improves one’s abilities, but without the innate competence one is unlikely to be successful.
There are a number of institutions that offer training in different types of language practice and although not essential to becoming a good translator, etc., it is a good idea to take a course or two. This gives one some theoretical grounding and today the courses generally include a fair amount of practical work as well, which is invaluable.
Download 2019 list of training in the language professions