How can to know if my s4 has a locked or unlocked bootloader ?
If you have the non-developer edition of the Galaxy S4 on Verizon or AT&T it's locked. These would be model numbers SCH-I545 or SGH-I337. If you have any other version of the S4, it's unlocked.
I have i9500 so it's unlocked ?
Yep, it is indeed unlocked.
Since I have an GT-I9505, does that mean that my bootloader us unlocked or locked than???