Must be why I said standard.

No, that would be because you didn't know what standard keyboard layouts are.

* CAN/CSA Z243.200-92 is a standard keyboard layout. One Alt modifier, one level 3 shift: https://www.oqlf.gouv.qc.ca/images/ti/clavier.gif

* DIN 2137-1:2012-06 T3 is a standard keyboard layout. One Alt modifier, one level 3 shift: https://de.wikipedia.org/wiki/Datei:German-T2-Keyboard-Proto...

* ABNT NBR 10346 2 is a standard keyboard layout. One Alt modifier, one level 3 shift: http://www.windowsintegral.com/wp-content/uploads/Teclado_AB...

You're taking what I said too literally. If you go to a store and buy an off the shelf PC, a very common keyboard will come with it that has 2 ALTs.

I've never lived anywhere where that'd be the case.

Incorrect. That is not what happens when I do that.

And which layout would that be?

Because it's not standard in fairly large parts of the world.

I don't know whether or not the presence of a right Alt or Alt Gr instead is most common worldwide, it seems you do. Do you have a source?