Not S E Asian but as Teodor says is Omani or that region. A bit big I think for a Shafra but there is a larger version (which I think yours is) which is worn in the belt or sash. The exact name of the larger one escapes me but I am sure someone here will know.
Stu
Have done a bit more digging. This knife is called Al Kusha....refer
http://www.vikingsword.com/vb/showth...ighlight=kusha
The shafra blade is (generally) straight rather than curved.
Stu