Bret was huge in places like Europe, but I don't know if it makes him the biggest international star ever though.
To make such a claim you'd need to do your research on other huge stars as well as for Bret.
For example, I don't know how many World tours Austin participated on during his height of fame - but I'm fairly sure if he travelled as much as Bret he'd have drawn great crowds the World over in '98/'99.
Austin Drew than Bret Internationaly Than Bret hart.
Mayhem in Manchester - Manchester, England - Nynex Arena - April 4, 1998 (18,514; sell out)
WWF @ Obenhausen, Germany - Arena - April 5, 1998
WWF @ Berlin, Germany - Deutschlandhalle - April 6, 1998 (8,000)
WWF @ Beyereuth, Germany - Oberfrankenhalle - April 7, 1998(12,000)
WWF @ Hamburg, Germany - Sporthalle - April 8, 1998
WWF @ Vancouver, British Columbia - GM Place - July 4, 1998 (12,746)
WWF @ Toronto, Ontario - Skydome - August 1, 1998 (14,688)
WWF @ Montreal, Quebec - Molson Centre - August 2, 1998 (11,209)
WWF @ Calgary, Alberta - Saddledome - September 11, 1998 (14,017)
WWF @ Toronto, Ontario - Skydome - February 8, 1999 (41,432; 38,661 paid)
WWF @ Oberhausen, Germany - Arena - April 1, 1999 (7,048)
WWF @ Sheffield, England - Arena - April 2, 1999 (12,744; sell out)
WWF @ Newcastle, England - Telewest Arena - April 3, 1999 (10,699; sell out)
WWF @ Birmingham, England - NEC Arena - April 4, 1999 (12,236; sell out)
WWF @ Vancouver, British Columbia - GM Place - April 16, 1999 (14,599)
WWF @ Calgary, Alberta - Saddledome - April 17, 1999 (15,419; sell out)
WWF @ Edmonton, Alberta - Skyreach Centre - April 18, 1999 (16,874; sell out)
WWF @ Toronto, Ontario - Skydome - April 23, 1999 (17,402)
WWF @ Toronto, Ontario - Skydome - July 24, 1999 (15,220)
Bret drew 3000-4000 Per average Austin drew Much More.
http://www.thehistoryofwwe.com/99.htm