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Those are the primary, general four languages, but other languages are used as necessary for specific domains (e.g. Javascript, Objective-C/Swift), they're just not guaranteed to get the same level of internal tooling and infrastructure support (though in practice they do).

That's actually an error in the paper -- JavaScript is now an officially approved programming language at Google.

Clearly there is some use of Dart and JavaScript (vanilla, Angular and Polymer). It would be interesting to hear percentages across Google development.

http://www.gwtproject.org/

Slightly tongue in cheek (since Google obviously uses javascript), but Java :)

The only 4 languages I known. Awesome!