If you are working on a distributed development project with teams in countries speaking the same language(For example English, between India and US), you won't face much of problem. But if you are working in a different environment otherwise (Say, between India and Germany OR India and France, etc where they don't speak the same language), you would need to keep the language barrier in mind during estimation. (This sentence is really mouthful !!!)
For example, you might receive a requirement document in German. The customer in Germany assumes that you would do the translation to English before writing the test cases or whatever. The problem here is, the same customer also assumes that as soon as you receive the requirement document you would start the work. Which is not really so.
This is how it works: Let us say the customer hands off the requirement document on Monday, and it takes nearly 3 days to translate the same to English(or local language). (Assuming that you have an inhouse translator). Then ensure that you keep this buffer in mind while doing the estimation. Not only that, if you have a poor translator it would add much more chaos.
Testing team needs to be very cautions in this situation. Sometimes, the testing team might have to struggle for days to get the actual requirement translated to their local language, before writing the test cases. This might add undue pressure on testing team during release days.
Couple of solutions:
1. Try to have as many face to face interactions and conversations as possible with the customer. Try to write the test cases based on "Drop-in meeting" principle. Basically, you can keep updating the test cases in small iterative cycle after every conversation with customer.
2. Bring the culture of using acceptance testing framework like FIT into the team.