Nokia Lumia 520 - Can I make Skype calls using my Lumia phone?

Yes, it is available in the Store. It is free to download, but operator charges may apply if you use a mobile data connection.

The Skype for Windows phone app will support the following languages: English, Danish, Dutch, Finnish, French, German, Italian, Japanese, Korean, Norwegian, Polish, Euro Portuguese, Brazilian Portuguese, Russian, Simplified Chinese, Spanish, Swedish, Traditional Chinese and Turkish.

Note that Skype is not available any more for the Windows Phone 7 devices. The supported platforms can be found at the Skype support site.