1)
How did they put their mouths in Shamayim?
1.
Rashi (8): Refer to 73:8:3:1.
2.
Radak: They say that Elokim does not know about them.
3.
Radak citing his father: The root of "Shatu" is Shoses (spilling), i.e. their mouths run in Shamayim.
4.
Malbim: They announce opposite to what was said above.
2)
Why does it say "u'Leshonam Tihalach ba'Aretz"?
1.
Radak #1: Their mouths and tongues go in the land, and they put them in Shamayim.
2.
Radak #2: They speak [improperly] about Elokim in Shamayim, and about people who fear Elokim in the land.
3.
Malbim: In the land they do not hear what was said above. Only their tongues are heard in the land.