There’s a handful of games on Nintendo Switch Online that you need to download the Japanese version of the apps to play. Here’s a guide to what’s available and how playable it is if you don’t know Japanese. Some of it’s really good stuff! I’ll try to keep this thread updated based on what is released.
Famicom
Adventures of Lolo 2
- Japanese required: None
- Note: This game was released in North America and Europe as “Adventures of Lolo 2.” The game titled “Adventures of Lolo” in North America and Europe was not released at all in Japan, so in Japan this is simply titled “Adventures of Lolo.”
Clu Clu Land: Welcome to New Clu Clu Land
- Japanese required: None
- Note: This is an updated version of Clu Clu Land that was released for the Famicom Disk System.
Famicom Mukashibanashi: Shin Onigashima
- Japanese required: Story based, lots of text.
- Note: A two-part long adventure game for Famicom Disk System.
Famicom Wars
- Japanese required: Lots of menus
- Note: The first game in the “Advance Wars” series.
Fire Emblem: Shadow Dragon and the Blade of Light
- Japanese required: Story based, lots of text
- Note: The first in the Fire Emblem series, an official translation was released but is no longer available for sale.
Gomoku Narabe Renju
- Japanese required: None
- Note: A Famicom interpretation of the board game Gomoku Narabe
Mahjong
- Japanese required: Mahjong knowledge and terminology required
- Note: Nintendo’s first Mahjong game for a home console, very basic.
Route-16 Turbo
- Japanese required: None
- Note: A remake of a 1981 arcade game. Very simple but fun driving maze chase game.
Smash Ping Pong
- Japanese required: None
- Note: Released in Europe previously as Konami’s Ping Pong.
Tsuppari Oozumou
- Japanese required: Some, mainly just menus
- Note: A sumo game that’s very famous in Japan.
Yie Ar Kung-Fu
- Japanese required: None
- Note: Never officially released in the west but a staple of pirate cartridges and systems.
Super Famicom
Fire Emblem: Genealogy of the Holy War
- Japanese required: Story based, lots of text
- Note: The fourth game in the Fire Emblem series.
Fire Emblem: Mystery of the Emblem
- Japanese required: Story based, lots of text
- Note: The third game in the Fire Emblem series.
Kunio-kun no Dodgeball da yo Zen’in Shūgō
- Japanese required: Some, mainly just menus
- Notes: A sequel to Super Dodgeball for NES.
Marvelous: Mōhitotsu no Takarajima
- Japanese required: Story based, lots of text.
- Note: Adventure roleplaying game. First game directed by Eiji Aonuma.
Shin Megami Tensei
- Japanese required: Story based, lots of text
- Note: The first game in the Shin Megami Tensei series.
Shin Megami Tensei II
- Japanese required: Story based, lots of text
- Note: The second game in the Shin Megami Tensei series.
Shin Megami Tensei if…
- Japanese required: Story based, lots of text
- Note: A spinoff of the Shin Megami Tensei series, often considered to be a precursor to the Persona series.
Sugoi Hebereke
- Japanese required: Some, mainly just menus
- Notes: A top-down vs. fighting game staring the characters from the Hebereke game series.
Umihara Kawase
- Japanese required: None
- Notes: The first game in the Umihara Kawase series, a puzzle platformer where you play as a girl with a fishing rod.
Nintendo 64
Custom Robo
- Japanese required: Story based, lots of text
- Notes: The first game in the Custom Robo series. The game released in the West as Custom Robo is Custom Robo 3.
Custom Robo V2
- Japanese required: Story based, lots of text
- Notes: The second game in the Custom Robo series.
Harvest Moon 64 (Announced, not yet released)
- Japanese required: Story based, lots of text
- Note: Natsume owns the Harvest Moon name and Marvelous owns the games so it’s unlikely this will ever be released in English on NSO. More information on the IP here.
Game Boy
Yakuman
- Japanese required: Mahjong knowledge and terminology required
- Notes: A Game Boy launch title in Japan, play mahjong either against the computer or with other players.
Kaeru no Tame ni Kane wa Naru
- Japanese required: Story based, lots of text
- Notes: A precursor to The Legend of Zelda: Link’s Awakening. Known as The Frog For Whom the Bell Tolls.
Game Boy Advance
Fire Emblem: The Binding Blade
- Japanese required: Story based, lots of text
- Notes: The sixth game in the Fire Emblem series.
Mother 3
- Japanese required: Story based, lots of text.
- Notes: What can I cay, it’s Mother 3
EDIT: Added images