Rashi: When they come to tell with their mouths, they fabricate false exaggeration, even to change what is known to people. When they stick out their right hand for a Shevu'ah, they refrain from Shav, lest he be caught as a thief (one who steals via lying). Rather, they swear Sheker (people do not know that it is false).

Radak: Kings of the nations are haughty over me with their mouths, and say 'we will do such and such to him.' Their words are Shav, since you promised. Their right hand, i.e. their strength and Gevurah, is false strength and nothingness.

Malbim: Their mouths deny Your Hashgachah, and attribute everything to chance. Via this, their right hand is Sheker - they choose idolatry.