Your dominant language is the language that is strongest, the one you feel most comfortable speaking, reading, and writing. Your dominant language is usually, but not necessarily, your first language.

Professional translators translate into their dominant language because they are better writers in their dominant language. They translate from their non-dominant languages. So the source text is in your non-dominant language and the target text is in your dominant language.

If the project matches your languages and the direction you translate into, then you will want to inquire further about the project requirements.