How to validate NLLanguage values for NLLanguageRecognizer?

I expected the initializer NLLanguage(rawValue: "...") to return nil if I gave it junk, but it doesn't. It accepts any string. I'm loading values from a database so I'd like to know if I'm getting one that is valid, like "en", "es", etc., as opposed to an error. Is there anyway to check that?

I'm using it to set NLLanguageRecognizer.languageConstraints, so I guess by "valid" I mean all the languages that work with that property.

The struct has a bunch of static constants:

struct NLLanguage {
    static let english = ...
    static let spanish = ...
    ...
}

If those all work with NLLanguageRecognizer I guess I can paste them all into a dictionary.