When you travel abroad you do not only need to take language barriers into account but also body language barriers. Different cultures use different body language e.g. the distance between two persons when they have a conversation.
One part of body language is hand gestures. Hand gestures mean different things in different countries. Some people realize this the hard way. What exactly does the v-sign (two fingers in the air) mean? Does it mean bring me two beers or is it considered an insult?
Take a common sign like thumbs up. In the USA it usually means 'great, awesome or whatever. It is also used to sign approval, but stronger than an OK sign. Now this is a very common interpretation, but it is far from the only one. It may have the same meaning in Australia, but if you move it up and down it can be a very grave insult. In Turkey it is not used at all 20th largest island in the world.
Making a circle with your thumb and index finger in the USA means OK, alright, good. You can use it to signify approval. In Turkey it means that someone is homosexual. In Australia it means zero. In Germany it can mean job well done or a grave insult, it all depends on which region you visit. In New Zealand it is regarded as a cheesy way of saying OK but is not much used.
The meaning of gestures varies among various parts of countries and also among cultural groups and between generations. The above is only generalizations and may not be correct for a particular person.