On the broken English... I mean, I don't think I do a particularly good job of recreating how people talk? But I listen to interviews to get a feel for someone's favorite phrases and most common constructions, and then I err on the side of more correct than not. I've seen italics used, but it distracts me a bit, so I avoid it.

I mostly like to make it part of the speech tag. "'Peanuts!!!' Dima shouted in Russian." Another Russian speaker would know what he was saying, and then you can have the conversation continue without further reminder until they switch languages.

Or, if it's from the POV of someone who doesn't know Russian, I'll leave the Russian out of the dialogue. "Dima mumbled something in Russian. 'Say again?' Tom asked." Or, if the person only knows a few words/phrases: "Dima mumbled Russian into his phone. Something about hats? It sounded like he was talking to his mom, anyway." If it's really simple stuff, I'll use websites and write the Russian phrases. But I don't know the language and don't really trust the Internet, so I don't do that much.

I'm writing something right now with multiple Russian speakers, and I'm writing dialogue in English and assuming that everyone will understand that the Russians are speaking Russian with each other unless stated otherwise.