1)
What is the meaning of "Tabanah"?
1.
Rashi: They will speak. Radak - this is like "Yabi'a Omer" (19:3). "Tabanah" implies constantly speaking, like a source [of a spring] that flows without ceasing.
2)
Why does it say "Selamedeni Chukecha"?
1.
Radak: When You will teach to me Your Chukim, I will constantly praise You with my lips.
2.
Malbim: He already prayed six times and said "Lamedeni Chukecha." Now, at the end of his Tefilah (the seventh - "Sheva ba'Yom Hilalticha" (164)), he is sure that Hashem will fulfill his request, and thanks that He [will] teach to him Chukim.
