For people asking about the Wonderswan/Color, there are actually quite a few good games that are completely playable for non-English speakers. Problem is, some are really expensive. But you could still import a WSC and a handful of great games for dirt cheap on eBay.
Golden Axe, Rock Man and Forte: Challenger from the Future, Gunpey, Gunpey EX, Space Invaders, Judgement Silversword, Guilty Gear Petit, Guilty Gear Petit 2, Pocket Fighter, Rhyme Rider Kerorican, Makai-Mura (WS exclusive Ghosts n Goblins), Digimon Frontier: Battle Spirit, Digimon Tamers: Battle Spirit, Final Lap Special, Mr Driller, Klonoa: Moonlight Museum, Rockman EXE WS, SD Gundam: Operation UC, Tetris, Ultraman, One Piece: Swan Colosseum, Kinnikuman Nisei: Dream Tag Match, Beatmania, Buffers Evolution, Crazy Climber, Digimon Adventure: Anode and Cathode Tamer Veedramon Version, Fire Pro Wrestling, Puyo Puyo, Puzzle Bobble ... Not all of those are great, but I own them all and they're all playable without Japanese knowledge (as long as you don't mind missing out on story segments in some games).
If you dig the Wonderswan Color I recommend tracking down a SwanCrystal. The screen is way, way better. Comparable in quality to the NGPC's, maybe better.