Is notarizing and translating documents a common procedure for obtaining a non-B visa in Thailand?

A big concern is that you didn't buy the transcript on KhaoSan road. That is the reason for the strict notary.

Translation is the minimum. Depends on the immigration officer whom can ask for legalisation, or can skip it (usually when you come with your files translated in the first place).

Once they ask for it you should get it done.

From my country the full legalisation process here is :

Go to embassy in bkk with all documents that needs to be legalised, they don’t do it for every kind of documents but national diplomas yes.

You pay for 1St stamps.

Then you bring them to a translation shop appointed by the embassy.

You pay.

Then brings them back to embassy and pay again to legalise the Thai translation of your documents (not kidding).

Then, you can move on to the MRT office of the Thai foreign affairs ministry (check but I thing it is queen sirikit or klong Toei station) and ask for final Thai legalisation of your documents.

Then pay again but half cheaper than my embassy’s legalisation.

Takes time...

Your officer may or may not accept documents done halfway with just your embassy legalisation. I had both cases as documents accepted with only translated but not legalised documents.

Stay strong.

That is standard, but you better check on who they accept as notarizing it is your transcript, as it has been required that it comes directly from your university. It is not notarizing that the translation is correct, but that it is in fact your transcript. Check with immigration to find out what they accept for the notarized copy.