Psalm 147:20, "He has not done this for just any nation; they do not know his ordinances. Praise Yah!" means that God has uniquely favored Israel by revealing His laws and commands to them. Other nations have not received this special revelation.

Here's a breakdown of the meaning:

"He has not done this for just any nation...": This emphasizes the unique status of Israel. God has chosen to bless them in a way He hasn't blessed other nations.
"...they do not know his ordinances.": "Ordinances" refer to God's laws, statutes, decrees, and instructions. The verse points out that other nations are ignorant of these divine laws, implying they are not in the same covenant relationship with God as Israel.
"Praise Yah!": This is a call to praise God (Yah is a shortened form of Yahweh, God's name) for this unique blessing bestowed upon Israel. It is a declaration of gratitude for God's favor and revelation.

In essence, the verse highlights:

God's special relationship with Israel: This verse supports the idea of Israel being God's chosen people, entrusted with a unique role and purpose in His plan.
The privilege of knowing God's law: Having God's law is presented as a significant advantage, providing guidance and a path to righteousness that other nations lack.
The call to praise God: The appropriate response to God's favor is praise and thankfulness.

Different Interpretations:

Some interpret this verse to support the idea of Jewish exceptionalism or superiority.
Others see it in the context of salvation history, where God used Israel to reveal Himself and His laws to the world, ultimately leading to the coming of Jesus Christ, through whom salvation is available to all nations. This perspective emphasizes that while Israel was initially uniquely favored, God's ultimate plan includes all people.

Regardless of the specific interpretation, the verse clearly emphasizes the unique blessing of knowing God's law and the corresponding call to praise Him for it.