falando do diabo, ele aparece! como dizer isto em Inglês?

This must have happened to you more than once. Here you are talking to someone about a mutual friend of yours that has been very absent lately. Just when you're finished talking about him or while you're still talking about him, he appears out of nowhere and leaves you in shock. In a way of acknowledging his unexpected arrival, you say: speak of the devil!

That's a short way of saying "speak of the devil and he will appear". You don't mean in any way to offend that person by calling devil. That expression lost its dark satanic connotation a very long time ago. It's just a way of expression how you feel about the coincidence that just happened. And just one more thing: the verb can be both speak and talk, as in talk of the devil. Take a look at this example:

Alan: I haven't seen Bob for weeks. Jane: Look, here comes Bob right now. Alan: Well, talk of the devil. Hi, there. We were just talking about you. speak of the devil and in he walks.