Determine how comfortable you are with foreign languages. Most places have at least a few people who speak English in the tourist areas, otherwise you may have to resort to smiles and sign language. Some countries do not use the Roman alphabet, such as Russia, Ukraine, Serbia, China, Japan, so don't count on reading the signs and looking up the words in a pocket dictionary. Do a little research on your destination, find your linguistic level of comfort, and choose accordingly.
Also consider that if you are coming from the USA to a place like Britain, the language is still English, but with subtle differences that could confuse you.
At least learn a few basic words and phrases for your destination country, so you can say hello, please and thank you.
Photo Gallery Language For Your Travel Destination
Language For Your Travel Destination Images
Foreigners who cannot speak English will appreciate hearing a few polite words they understand. And even if they do speak English and will then converse with you in your own language, just making an effort to say thank you in French, German, Italian, Chinese, etc. Will make them more at ease with you.
There are online courses, some are free, which allow you to learn at least some conversational parts of a language, which are worth doing beforehand if you want to learn at least something of the language for where you are going. It also helps to watch movies made in the country you are going to in their own language, so you get a feel for the language and maybe the place as well, and how the people speak.