Deep Dungeon: Madou Senki English translation
魔洞戦記 ディープダンジョン · Deep Dungeon: The Heretic War
An English translation of the first Deep Dungeon, the 1986 Disk System dungeon crawler, given the English subtitle The Heretic War.
What's translated
The patch puts the game's Japanese text into English, so the crawl can be played without reading Japanese. The translators chose The Heretic War as the English rendering of the subtitle Madou Senki. Version 1.0 was released in April 2006.
The game
Deep Dungeon is one of the earliest console dungeon crawlers: you walk the corridors in first person, fight monsters in turn-based battles and slowly make your way down to the bottom floor. It was developed by Humming Bird Soft and released under Square's DOG label, and it started a series of four games.
Playing it
The patch is applied to your own copy of the Japanese Disk System game, following the instructions in its readme. The patch's database page linked here has the details.