Some people say that visitors should learn something of the local language and customs before travelling. I agree with this opinion to a great extent, although I accept that full preparation is not always realistic.
The most important reason is respect. When tourists make an effort to greet people in their language or to follow local etiquette, such as removing shoes in a temple or dressing modestly, the hosts feel appreciated and are generally more welcoming. Preparation also makes communication easier. Knowing a few phrases for ordering food, asking directions or saying thank you can prevent misunderstandings and open the door to friendlier conversations. Finally, it improves safety and enjoyment. A traveller who knows which behaviours are offensive, or what the local customs are for bargaining and tipping, is less likely to cause problems and can relax and take more from the experience.
There are some counter-arguments. In many tourist destinations, local people speak English, so visitors can manage without any other language. For short trips of a few days, it may seem too much effort to study a language that they will probably never use again, and some travellers visit several countries on one trip. Technology also helps, since translation apps can solve most immediate problems.
Even so, I believe a small amount of preparation is realistic for everyone. Learning ten or twenty useful words and reading a short guide about customs takes only an hour or two, and the benefit is out of proportion to the effort. Travel companies and guidebooks could include such information as standard.
In conclusion, tourists should learn basic phrases and customs because it shows respect, improves communication and makes the trip safer and more enjoyable, even if fluency is not expected.