I'm not sure exactly what you are trying to say without more context, If perhaps you are listing an important qualification for a job, you might say: "Competence in a foreign language is a priority" "Proficiency in a foreign language is a priority" "Mastery of a foreign language is a priority". "Competence' and 'proficiency' imply a working knowledge. 'Mastery' is closer to perfection.

Is the demonstration of language fluency a priority?