Most people can easily agree on what constitutes a poor translation, but agreeing on what constitutes a good translation is trickier to define!
With that in mind, here’s my definition:
In general, the purpose of a translation is to communicate the same message of the original text. The message could be instructions in a user manual. In this case, the translation must ensure that for example, a Spanish machine operator can perform the same actions as a Danish operator and that no accidents occur. This means that the translation must stay as close to the original text as possible. It must not be a creative translation. In another text, for example in a company website, the message of the text may be to convey that a company is credible and professional. In this case, a freer, more creative translation may be required to be able to convey the message to a reader in another country.
In every case, the aim is to ensure that everyone has the same “experience”, regardless of whether they read the original text or a translation of the text. Accordingly, it is not enough that the translation is technically correct. In the case of a superior translation, the reader does not even notice that the text was translated; that the original text was written in another language.