I am learning Mandarin (Chinese) and I must say it is a very enjoyable hobby for me. I will link to the tools that I am using below. The most recent one that I have found is a very nice translation feature in Internet Explorer 8. This is only one of the new features of IE 8 that I find to be fantastic.
You can highlight some text in any language and right click, or click the blue icon. Then you can hover over ?Translate with Live Search? and select the appropriate language. Viola! This is very helpful to me in my endeavor to learn Mandarin.
The tools:
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