There are several ways to represent how well you know a language on your CV. To write what your language level is in your own words, you can use one of the following terms:
Advanced: Proficient, fluent, native-level, bilingual, native, mother tongue, upper intermediate, full professional proficiency
Mid-level: Intermediate, working proficiency, professional proficiency, conversationally fluent, limited-working proficiency, written proficient
Beginner: Elementary proficiency, basic-working knowledge, pre-intermediate, fundamental, introductory knowledge
Remember that the language-level terms in this list don't all mean the same thing. For example, being proficient in a language is not the same as being fluent in it. Proficiency means that you have complete mastery of a language. In contrast, fluency is the ability to speak with ease in any situation, though you might sometimes have limited vocabulary.
Check that the terms you use to write your language level accurately reflect your ability in that language.