To answer this question properly, it's best to explain first what a "dub" is. In video games publishing, a dub is a game, usually produced and developed in Japan, the audio for which has been translated and dubbed into English or other target languages for new intended markets.
Dubbing a game is part of the publisher's translation and localization process. Specifically, dubbing involves translating all voice acting and other speech and voice assets from the original game, adapting it for the local market (including any cultural adaptations, as deemed appropriate by the publisher), hiring new voice actors, re-recording the new audio in a studio, and integrating it in the game.
An undub is a game in which the dubbing of the voice assets (but not graphics or text) is reverted back to Japanese.
Just like a large number of people prefer to watch foreign films with subtitles in the original language, fans of video games feel the same way about playing their games. Unfortunately, unlike movies, video games are rarely shipped with multiple audio tracks which would allow the user a language choice. While multiple-language audio is not uncommon in Europe where even the Japanese track is often left intact, U.S. publishers are notorious for stripping out all Japanese audio and replacing it with a substitute track that they have produced themselves.
While the director of the game can influence the original voice actors, explain character personalities to them, and generally set the tone for the work, that opportunity is lost when the game is taken overseas to be localized.
To make matters worse, the quality of the voice acting in the United States is much lower than it is in Japan. Although much of the world's acting talent resides in the United States, a very small portion of it prefers to do voiceover work, whether it's for video games or cartoons. By contrast, Japan, with its proud legacy of made-for-TV animation has a huge arsenal of quality actors (called seiyuus) whose sole career focus is voice acting. Popular seiyuus often record spoken-word CDs, called "dramas," and even perform monologues on stage at live events! Many seiyuus have huge fan followings, a phenomenon almost completely unheard of in the West.
No, although they often cater to the same audience. As with undubbing projects, fan translations also leave the Japanese audio track intact, but they have a much larger task of translating text, including all storylines and dialog, as well as menu items. Translations require work of a dedicated team, often consisting of multiple people with divided translation and hacking responsibilities (sometimes with different hackers for text and graphics), and often take several months or even years.
Undubs, on the other hand, can often be completed by one person without extensive hacking skills. The scope of an undub is limited by nature: all the text has already been translated, and the Japanese audio exists either on original Japanese media or hidden somewhere in the file system. Depending on the complexity of the game's structure, undubs can be finished in anywhere from under an hour to a few days.
If you own the copies of games, no one can stop you from hacking their contents or discussing with others how to do it. If you are using audio assets from a Japanese version of a game, you probably have to own both the English and the Japanese copy of the game, due to complexities of copyright law that are beyond the scope of this FAQ.
If you are distributing an undub that includes copyrighted assets, you are probably breaking the copyright law of Japan, the United States, and most other countries. Distributing games on Undubbing.com is not allowed. Violators will be banned without warning.
Interestingly, this question often comes up in forum discussions. Some people in the video game industry (who are often vocal on NeoGAF) believe that you somehow offend the localization producers and voiceover actors by reversing their work and substituting it with the original Japanese audio track.
Our position is that even if someone makes an argument that undubbing is disrespectful to the localization team and their contractors, it's probably not as disrespectful as the publisher's efforts to throw away the original work of the game's creators and seiyuus and substitute it with a mediocre dub.
Another commonly heard argument is that people who prefer undubs are Japanophile snobs who pretend to be better than everybody else by watching anime or playing games in Japanese without understanding any actual Japanese.
Our response is usually just to point to the movie industry and its acceptance of watching foreign movies with subtitles, whether the viewer understands the language or not. Subtitles coupled with original audio has become the de facto translation format for foreign films, and we insist on the same for video games. Actors' vocal expressions are such an inseparable part of the original work that substituting them with anything else is unacceptable, even if the director does sometimes give in to distributor demands and sanctions a dub.
One exception we can think of where dubs are acceptable are games or cartoons that are intended for a very young audience who would not receive subtitles well. Pokemon is probably one such series.
Incidentally, dubs sponsored by Disney are usually top-notch work, and we enjoy them as much as we enjoy the originals. Which dubs do we not enjoy? Naruto.
Foreign speech and accents often seem attractive to us, even (and especially) if we don't understand language. Is that why so many people believe that undubs are better?
Because we actually speak Japanese, we can actually answer this question with ease. The answer is no. Most English dubs actually suck, whether you understand Japanese or not. The more fluent you are in both languages, the more you appreciate the awesome professionalism of Japanese voice actors.
If more English dubs are voiced by Eddie Murphy or Mike Meyers, maybe we'll change our mind.