Boardgamegeek https://boardgamegeek.com/boardgameexpansion/2807/catan-5-6-player-extension
English - Allows you to add up to two more opponents to The Settlers of Catan. The only change in the rules is that there is a building round at the end of each turn in which any player can build.
Ludovox http://ludovox.fr/jeu-de-societe/les-colons-de-catane-extension-56-joueurs-339/
French - Un jeu de Klaus Teuber.