Dirk Nowitzki Starts U.S. Citizen Process, Getting a Green Card!!

Getting a Green Card!!

The Dunking Deutschman is goin' American ... 'cause Dirk Nowitzki has officially started the process to become a U.S. citizen!!

The recently retired 40-year-old Dallas Mavericks superstar and his Swedish wife, Jessica Olsson, are working on getting their green cards together ... which is the first step in a VERY long process to becoming a citizen.

"So once we accomplish that, then you have to be a green-card holder for, I think, over five years before you can even think about doing that [becoming a U.S. citizen]," Dirk told the Dallas Morning News.

"So we're going to do that and see how it goes. But obviously our [three] kids were born here and they all have U.S.…