Today I needed an authorization letter notarized for a visa my daughter is applying for. Since I speak the language of the foreign country, I used that language for the letter. And when I went to my usual notary, he refused to notarize it because it is not in English (or, more properly, I guess, because he cannot understand the language).
After a brief search, it looks like this is fairly standard. But my question is why. Looking online, I find phrasing such as
The notary public is a commissioned representative of a state government and is charged with verifying your identity as the signer, ensuring you sign under your own free will, and witnessing the signing event.
Doing that doesn't require understanding the contents of the document. Other sites, including the corresponding the Wikipedia article, list steps that a notary should take, and none mentions "reading the document and understanding it".
So, the question is
Why is the notary required to understand the document I present him, when all that needs to be done is to certify that my signature is mine?