However the only limitation of the feature was that it was only available for Skype-to-Skype calls. The good news is that has changed, according to a blog post by Skype (via The Verge) in which they have announced that the feature will now work for calls made to mobile phones as well as landlines.
According to Microsoft, “Since its introduction in 2014, Skype Translator has made it easier for you to connect with people around the world on Skype no matter where they are. We love bringing people together, and so today, we’re excited to announce the next milestone for Skype Translator: voice translation for calls to mobiles and landlines* on Skype Preview. You can now use Skype to call people on their phones and communicate across languages, even if they do not have Skype.”
However according to the announcement, you will need to sign up for the Windows Insider Program first in order to access this feature. You will also then be required to have the latest beta of Skype installed, and purchase some Skype credits in order to make the calls. Once you’ve done all that, you should be good to go.