OpenType Pro fonts share the same technical specifications as OpenType Standard (OT) fonts, but support a broader range of languages. Standard OT fonts contain support for Western languages, while Pro fonts include Central European, and often Greek and/or Cyrillic and Extended Cyrillic. 

Read more here: FontFont OpenType Formats Explained

Here’s the OpenType FontFont language support table from the PDF leaflet for your handy reference (updated on December 17, 2010):

» Download the table as a PDF