Everybody would understand what you mean if you say it in the way that you suggest. However, if you want to be more precise then you could use the nomenclature (the specific system of names given in a field) that is used in the language field... these are simply letter and number combinations from A1 (the most basic level) up to C2 (the most advanced level). A native speaker has a C2 level in their own language. The vast majority of people never achieve a level higher than C1 in a foreign language... but C1 is, itself, a very good level.