1)
Why will he praise Hashem among the nations?
1.
Radak: It is for all this (Radak Shmuel II, 22:50) - He saved him from men of violence, and elevated him over his enemies and gave him vengeance against them.
2.
Malbim: It is to thank Him for the good.
2)
Among which nations will he praise Hashem?
1.
Radak: In front of the nations that heed me and serve me.
2.
Radak (Shmuel II, 22:50): In front of every nation.
