They got stuck on ethics and gave up even trying to make any recommendations, though, so I'll step in.
1) Don't be a dick. Do not do things that make other people's lives harder just because you are curious about them. Don't trample the local culture.
2) Nothing about us without us. Involve the people you are working with. Listen to them. Respect their choices.
3) Give back. Don't come in and take what you want without returning anything for it. This makes it an exchange rather than misappropriation. If you're worried about messing with the data, weed a garden or donate some food or whatever people need at the moment.
4) All languages are valuable. Don't come in and try to stamp it out because you wish people would use some other language. It does not matter why. It is none of your business what language other people choose to use. They may not even care about talking to you. You may tell them about other languages, but it is wrong to pester them and evil to force them to switch. See Rule #1.
5) Don't bait and switch. It is cruel to offer something and then not deliver. This may be a particular issue in poor and isolated Deaf communities if the topic of medical care or adaptive equipment comes up. If you think you're going to need something, or the local people might need it, then make sure you can secure a supply. If there is no feasible way to get it, then leaving it unmentioned may do less harm than mentioning it.
6) Don't withhold information or lie to people. This may be challenging to balance with Rule #5 but is essential regarding Rule #1. Primarily this means if someone asks about something you have not mentioned for reasons of Rule #5, it is time to share what information you have.
7) Remember that these are live people, with feelings, not a science experiment. Of course they are fascinating. Keep your enthusiasm within reasonable bounds and mind your ethics as best you can. Don't act like a mad scientist. You and your hosts are fellow explorers of human nature; you are equals. Act like it.
Yeah, this upends centuries of scientific custom, but sometimes science needs a kick in the can from humanities.