Thanks everyone!
Interesting point about the fan translation of Chaos;Head. I am trying to compile a list of Japanese adventure games and visual novels that have been translated to English, either by fans or through an official release. I am trying not to focus too much on visual novels alone since there are thousands of them available nowadays, but Chaos;Head is one of the titles that got me intrigued. Still, I am trying to keep the most famous VNs on my radar. Also note that I only mention on the list the platforms where there is an English version of the games available for. Here is the list so far:
999: Nine Hours, Nine Persons, Nine Doors (DS)
Ace Attorney Investigations: Miles Edgeworth (DS)
Again (DS)
Another Code: R – A Journey into Lost Memories (Wii)
Apollo Justice: Ace Attorney (DS)
Banshee's Last Cry (iPhone)
Case Closed (Wii)
Chaos;Head (PC)
Clannad (PC)
Corpse Party (PSP)
Corpse Party: Book of Shadows (PSP)
Danganronpa: Trigger Happy Havoc (Vita)
EVE: Burst Error (PC)
Ever 17: The Out of Infinity (PC)
Famicom Tantei Club Part II (SNES)
Fate/hollow ataraxia (PC)
Fate/stay night (PC)
Hatoful Boyfriend (PC)
Higurashi: When They Cry (PC)
Hotel Dusk (DS)
Jake Hunter: Crash and Burn (iPhone)
Jake Hunter: Detective Chronicles (DS)
Jake Hunter: Memories of the Past (DS)
Jake Hunter: Seaside City Conspiracy (iPhone)
Katawa Shoujo (PC)
Last Window: The Secret of Cape West (DS)
LifeSigns: Surgical Unit (DS)
Love Hina (GBA)
Love Plus (DS)
Lux Pain (DS)
Never 7: The End of Infinity (PC)
Phantasy Star Adventure (Game Gear)
Phantasy Star II Text Adventures (Mega Drive/Sega Genesis)
Phoenix Wright: Ace Attorney (DS, Wii, iPhone, 3DS)
Phoenix Wright: Ace Attorney: Dual Destinies (3DS, iPhone)
Phoenix Wright: Ace Attorney: Justice for All (DS, Wii, iPhone, 3DS)
Phoenix Wright: Ace Attorney: Trials and Tribulations (DS, Wii, iPhone, 3DS)
Policenauts (Playstation)
Portpia Renzoku Satsujin Jiken (NES)
Princess Debut (DS)
Professor Layton vs. Phoenix Wright: Ace Attorney (3DS)
Radical Dreamers (SNES)
Remember 11: The Age of Infinity (PC)
Sakura Wars: So Long, My Love (Wii, PS2)
Saya no Uta (PC)
Shinpi no Sekai El-Hazard (GBA)
Snatcher (Sega CD)
Steins;Gate (PC)
Theresia (DS)
Time Hollow (DS)
Tokimeki Memorial Girl’s Side: 1st Love (DS)
Tokimeki Memorial Girl’s Side: 2nd Kiss (DS)
Tokimeki Memorial Girl’s Side: 3rd Story (PSP)
Touch Detective (DS)
Touch Detective 2 ½ (DS)
Trace Memory (DS)
Umineko: When They Cry (PC, partial translation)
Zero Escape: Virtue's Last Reward (3DS, Vita)
I am getting really loose on the term "adventure" or "visual novel" here, since I have included LifeSigns, Princess Debut and Sakura Wars on the list. Also, there are some oddballs, such as El-Hazard, which was originally released for the Sega Saturn and PC, but then ported to the GBA and translated by a fan.
There are also some games that are not included on the list that puzzle me. Play Novel: Silent Hill was released for the GBA, and then ported to the Sega Genesis and translated to Russian. Also, there is Yuu Yuu Hakusho Gaiden, which was released for the Mega Drive in Japan and was being translated to English by a fan (there are a couple videos on YouTube), but apparently the project was dropped. Finally, there is Memories Off 6: T-Wave, which is available at the American iTunes store, but only in Japanese.