The purpose of a CV is to get you an interview. It's important not to lie, but it's also important not to 'down play' your chances or underestimate your abilities. 'Passive' is too weak. 'Rusty', whilst not suitable for a CV, does show your level of competence in English. You might say 'Working knowledge of.......', or 'Good oral skills, competent written skills', something like that.
Good luck !
- For Teachers