Just by adding a few registry entries in the Current User hive, you can have a conversation with a person in a different language and every sentence will be translated on the fly (on a window at the side of the conversation).

Copy the following to a text file and name it something.reg, double click, and you’ve got the new menu. (restart Lync if menu don’t appear at once.

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Source: http://msdn.microsoft.com/en-us/library/gg436843.aspx