#WikiBhasha is a tool developed by Microsoft research that brings a smart translation service to Wikipedia. What makes this service so good is that it understands and supports the way articles are normally created. Often a writer only adds snippets of an article to a target article.
When you translate, you only translate what you need. You then copy it in the target article and you can make any modifications necessary before you save the work that you have done.
There is quite an extensive FAQ as well.