Internationally, Slokar has played with Slovenia at the 1999 FIBA Europe Under-16 Championship, the 2000 FIBA Europe Under-18 Championship, the 2002 FIBA Europe Under-20 Championship, the 2005 FIBA European Championship, the 2007 FIBA European Championship, the 2009 FIBA European Championship, the 2011 FIBA European Championship, the 2013 FIBA European Championship, the 2015 FIBA European Championship, the FIBA World Olympic Qualifying Tournament for Men 2008, the 2006 FIBA World Championship, the 2010 FIBA World Championship and the 2014 FIBA World Championship.