It's probably impossible to detect ALL languages without training for them specifically, but there's good generalization happening. Our model is a unified model rather than a separate model per language. We started out with language-specific models but found that the unified approach yielded slightly better results in addition to being more efficient to train.
I'll let Henry elaborate here, but we think there's a chance that a truly language-agnostic classifier is possible. That being said, the next version of this will support a few more languages: Ruby, C#, and Java.