Blizzard has finally announced a change that I think it long overdue. Before, if you had a friend you wanted to play with overseas, you weren’t able to. If that players was on a different server, there was no chance.
Global Play will allow players to easily switch between regions. Opening doors to mini games and gametypes that aren’t played in other regions. However, each region has it’s own separate data. Which means your profile, characters, rankings and friends list do not carry over. Your interface and your selected language won’t change.