In reply to Andrey Savchenko.

It appears that lots of plugins and themes are using this code in one form or the other.

Why is there no "deprecated" notice at least a few month before such a breaking change?

This change should be rolled back immediately, it probably affects millions of sites which did not even notice yet due to no monitoring at google or similar.

A weird quote can beo found here, "For the context while we consider date_i18() legacy function now", but there is not one word about that in Code Reference nor is there a doing_it_wrong migration hint or similar.

Something went pretty wrong with this commit, sorry to say.