Graphic design agencies need to think about many things when working with clients, as do Web designers. One thing that both career fields have in common is the challenge of doing work that can be globalized, and one of the major things to consider when it comes to this is language.
Translation presents a potential problem, as some words have no exact counterpart in another language. If you need to get words or phrasing translated from one language to another, it can be quite a challenge. So can slang. Some words won't make sense to those who don't use them on a regular basis. For example, if you are from the U.S., would you know that "bangers and mash" is something you eat?
Taking language into account in terms of the global Web market is a very smart thing to do. You can save both yourself and your client from embarrassment and make sure that you are getting your message across clearly. It just takes a little time to be sure you are saying things right--and it's well worth the effort.