Get rid of the limitation by Native Language. I can be as proficient in both languages.
It does not make sense to limit the native language to one language only. I can be as proficient in two languages. Mother tongue can belong to one country and having lived in a different country for over 20 years I can be as proficient in another language as well. I personally can switch from one to another on the fly without losing the train of thought. This is an impediment for your freelance members, which they cannot quote and the end customer will probably never understand the importance of "Native Language".