海外旅行、気をつけてね。って英語でなんて言うの？

In the first one: 'I wish you safe travels', you are using travel as a countable noun. This person is travelling by airplane and you are wishing wishing him/her well in all her travels. However you may also say 'Have Safe Travel' in which case 'travel' is an uncountable noun. When you say 'have a safe flight', you are wishing that person a safe flight on that particular airplane flight. 'Travel safely' is also appropriate when someone is traveling by airplane. This is usually used to wish someone safe travel either locally or abroad.

"Be careful" is the most sincere way to tell someone to stay safe on a trip. This phrase suggests that they may actually face some danger and that they should take action to protect themselves. If I have a friend going to the middle east or going sky diving I would tell them to "be careful." "Stay safe" is more general and is like a good luck wish of sorts. I would say this to any friend traveling, even just locally. "Don't do anything I wouldn't do" is a a common phrase that is often used as a joke. Tony Stark says this to Spiderman in Spiderman: Homecoming. It can mean, "don't take any risks," but its meaning changes depending on the person saying it. It's often said ironically. Have a great day! :D

"Stay safe" Used when you are letting someone know that they should stay safe and be careful. "Stay safe on your travels!" "Safe travels" Used more when someone is going to travel and they should be careful and stay safe!

Explanation: The above is the last thing you say to a person who is about to take a flight. It just means that you are wishing them a safe travel by flight. Some people do take offense to this final farewell as they think you are implying that they could encounter problems during this travel. So some people say 'have a good flight' instead of 'have a safe flight!'

Take care "abroad"...means "look after yourself" when you are away from your home "Abroad" refers to anywhere ...outside of your home ;-D It has also come to mean any "foreign destination"...and so whena friend is going on a trip we can say "TAKE CARE ABROAD"...to show we are concerned about their safety on the trip!.

The above phrase is a way of expressing that you hope your friend or relatives journey goes well.

All of these above express that said person wishes another person well while traveling overseas and to be safe.

Don't do anything I wouldn't do means what it says, but it's usually said as a joke by someone who does many things and has loose boundaries. Take care means be mindful of what your doing and take care of yourself. You should always trust your instincts, if something doesn't seem or feel right then it probably isn't, so don't do it!

informally you could say something like "stay safe" or "safe travels" if you would like to be more polite you could say "take care on your journey"

Safe travels' is probably the most common expression (and one I use all the time) to use when someone is travelling abroad and you want them to be safe. It has the same meaning as 'Have a safe trip' but in fewer words.

The sentences above mean that you are telling them that you hope that they reach their destination safely. Another word we can use for trip is journey.

It may be worrying if your friend is going to a dangerous place or somewhere where the country's normal level of personal security is not very good. "I'll send you a postcard from Mexico." "OK thanks - stay safe!" As a joke you may also say: "Watch out for the natives!" Definition native:'a local inhabitant. "New York in the summer was too hot even for the natives"

Traveling is fun and it opens our eyes to the beauty of the world. There is a lot we can learn on our travels around the world but traveling can also be dangerous because the world is full of people doing illegal and harmful things to benefit themselves. If we would like to wish someone a safe trip, the sentences above can be used. "Enjoy your trip Nyiko, please take care of yourself in Kenya." "Have a safe trip, my friend, I will see you soon, look after yourself and travel safely."