Stereotypica
The timeline called Stereotypica, in which everyone acts like their national stereotypes, first appeared in the AH.com Series episode “HOW SHARPER THAN A UNICORN'S HORN” In that episode, Thande appeared to have heard rumours of the timeline. The stereotypical-ness was caused by a virus, the Stereotypica Virus, which was cured by Torqumada at the end of the episode.
With some intervening hints, the Stereotypica Virus reappeared in the episode “HAIR TODAY, GOTTERDAMMERUNG TOMORROW”. In this we learn that the Virus was created by Justin Pickard as part of his nefarious plan, and has been used against many timelines, including Deutscherwelt, home of the Germans. The virus was cured once and for all at the end with Pickard's defeat, but there might be other undiscovered Stereotyped worlds still out there…