aller Herren Ländern

• aller Herren Länder (now more common)
• allen Herren Länder (proscribed)

Literally, “countries of all the lords”.

aller Herren Ländern

1. (set phrase, somewhat dated) everywhere; [from/in] many countries

   aus aller Herren Ländern kommen ― (please add an English translation of this usage example)

   in aller Herren Ländern sein ― (please add an English translation of this usage example)

The traditional (and grammatically correct) form is …Ländern (when used with aus or in that require a dative), but aller Herren Länder is now more common and treated as an exception in some grammars.

• “aus aller Herren Länder” in Digitales Wörterbuch der deutschen Sprache
• “in aller Herren Länder” in Digitales Wörterbuch der deutschen Sprache