When freelancing, is it better to brand yourself by language or feature?

For example, if you’re proficient in Java and Swift, does it make more sense to freelance as an “app developer, both iOS and Android” or a “Swift developer, iOS and MacOS apps”?

How do clients typically hire freelance work? By “app” or by language?

Advertising more languages may mean more potential customers, however customers may prefer a true specialist in one thing. Which to pick?