1) I played a good amount of untranslated Japanese ROMs for the NES/SNES/GBA, back in the day. Some of them had pretty simplistic gameplay ("Press A to swing your sword. Swing your sword until everything on-screen is dead.") or gameplay that was self-explanatory once it started. Those games didn't really need full translations to get enjoyment out of the game. Except, I recall a handful where I could never even get to the gameplay part because I was stuck in some pre-game menu hell where a non-native speaker would not be able to figure out how to get the game going, short of clicking every menu option and every sub-menu option. This happened alot with sports games, IIRC.
2) A more recent example that comes to mind would be Rhythm Tengoku (a.k.a. Rhythm Heaven) for the GBA. 95% of the game's gameplay is "Press a button in time with the rhythm", making it trivial for non-Japanese speakers to play. But one particular stage had an on-screen text prompt which told the player which button they should press at the right time, making it a random guessing game for the non-Japanese speakers. A quick translation for what is an incredibly tiny component of the full game would make a full localization unnecessary and still allow international players to complete the game.