Not necessarily; there are a few SNES games in the Switch Online library that weren’t localised and hence remain untranslated from Japanese, namely Super Puyo Puyo 2, Panel de Pon, Mario’s Super Picross, and Kirby’s Star Stacker. Though all of those games are puzzle games, which don’t necessarily need language to be enjoyed, whereas an RPG like Mother 3 would likely be much less enjoyable without understanding the dialogue, battle UI and so on.
“Why should I talk to you? I’ve just been talking to your boss.”