I checked with Monotypeimaging.com and this is the reply that I received from them when I requested a license for theCalibri family.
"Since you are not selling the eBooks and you’re using fonts provided with Windows 7 you won’t need any additional licensing. However, in the future when you start changing for the eBooks you will need additional licensing. Please hang on to my information and feel free to contact me directly when this happens and we can work out the specifics."
All the best,
Office# +1-212-389-6255 ext. 102
Translating books is a hobby of mine and currently, I pass it on at no charge.