From the Introduction:

White Wolf released the first edition of Werewolf: The Apocalypse in 1992, the second game in the World of Darkness setting. The game's titular Apocalypse arrived in 2004 and the game line officially ended and was replaced by Werewolf: The Forsaken, the second game in the rebooted World of Darkness.

Both games feature werewolves as protagonists in a World of Darkness, though the nature of that world has shifted between Apocalypse and Forsaken - as have the nature of werewolves themselves. Over the years since Forsaken's release, fans of both games have expressed the desire to bring aspects of one game into the other. Some want to use the streamlined mechanics of Forsaken to portray werewolves as doomed heroes against the forces of primal corruption. Others feel that the smaller scale of horror present in Forsaken is something they want more support for in their Apocalypse games. Some players want to mix bits of everything, incorporating the Tribes of the Moon, the Fera, the hisil, and powerful Garou warriors into the one chronicle to see what happens.

This translation guide exists to help people play Apocalypse with Forsaken rules, or vice versa. The tribes of both games are presented with the opposite game's rules, as are breeds, auspices, shapeshifting, character creation, Gifts, rites, and even the assumptions inherent to each game.