Add support for backend compatibility (#483)

[austindrenski]

Backporting per #607.

[roji]

Hmm, this definitely contains more than just the pure backwards compat feature - this is good example why it's important to separate refactoring and other changes into different commits. We ideally want to take only what is absolutely needed when backporting to a hotfix release.

But this looks safe enough I guess. OK for me.

[austindrenski]

I considered only bringing forward the compatibility portion of this, but then thought it was worth bringing the fix forward too since this was introduced to address the translation breaking behavior for 9.x.

But noted on keeping these commits more limited in scope.