Minimum requirement: fluency and in-depth knowledge and understanding of at least one other language and associated culture
This is the minimum requirement for employed and self-employed translators alike. The foundation a translator’s career is built on. How you acquire this fluency and knowledge is secondary. Not all translators have a degree in their second language, however, to be able to join a professional translators’ association – which is the minimum requirement for many agencies – they must have a degree and some sort of language qualification.
Some aspiring translators may have moved to a country and mastered the new language to a level comparable with that of a native speaker. They may have been brought up bilingually – the danger there is that the parent(s) teaching the child over time will lose touch with the living language, thus teaching the child an outdated version. For this reason it is important for a translator’s language skills to be verified through a formal process and for translators to join a professional translators’ association. There are plenty of low paying agencies who will take on unqualified translators, but no reputable agency will do so.
Ideally a translator will have lived in a country where their second language is the first language. They will have met local people and experienced their thought processes and reactions. If translating commercial documents it would be advantageous to also have experience of the foreign work environment and a country’s individual culture. And remember, although German is spoken in Germany, Austria and parts of Switzerland the cultural differences in these three countries are vast!