Which systems are region free (other than switch)
All pre-DSi Nintendo handhelds are region free. Even then, only DSi exclusive physical games are region locked, all five (?) of them. Not sure if you can read/speak/understand Japanese, but either way, you can't change the UI language on any Japanese model of DS to English.
PlayStation Portable and PS Vita are both region free and you
can change the UI language to English (functionality for X and O are flipped though). I highly recommend getting a PS Vita, especially the 2000 model, if you're at all interested in console hacking/homebrew.
Game Gear and Neo Geo Pocket (Color) are both region free. I don't believe PC Engine GT (Turbo Express) is region free. WonderSwan was only released in Japan.
Super Nintendo and Nintendo 64 are kind of region locked, but you can open them up and remove some plastic to play games from all regions.
GameCube is not region free out of the box. However, if you have a soldering iron and tools to open the console, you can bridge R6 on the motherboard which effectively turns a Japanese GameCube into a North American GameCube. Even the UI language will be in English. EDIT: You can also install a region switch, or if you’re feeling bold, you can install the XenoGC mod chip onto the optical drive’s logic board which lets you just play whatever region’s games as well as burned discs.
That's all I know off the top of my head.
Some really good Japan-only physical games
I picked up some Japanese only Game Boy games in the past couple months so here are my recommendations:
- Kaeru no Tame ni Kane wa Naru (The Frog For Whom The Bell Tolls) (Note: Prince Richard appears in Link's Awakening)
- Survival Kids 2: Dasshutsu! Futago Shima (Survival Kids 2: Escape the Twin Islands)
- Star Ocean: Blue Sphere
- Tomato Adventure (Note: From Alpha Dream, the developers of the Mario & Luigi series)
- Oriental Blue: Ao no Tengai
- Magical Vacation
- Samon Naito Kurafutosōdo Monogatari Hajimari no Ishi (Summon Night: Swordcraft Story - Stone of Beginnings)
- Shin Bokura no Taiyou: Gyakushuu no Sabata (Boktai 3: Sabata's Counterattack)
- Mother 1+2
- Mother 3
Most of these are RPGs.