Nobody gives a whoop about the N64 and half the people who do don't understand assembly code so it doesn't apply in that scene, but 'open' implies multiple developers.
I'm guessing that has to do because Japan was the least successful region for the N64, resulting in few Japanese exclusives (and thus, little interesting in the English translations scene
. Pretty sure if any non-English PAL games were released, it was limited to a couple sports game variations.).
From what I remember, Sin & Punishment (probably the most well-known of the exclusives, which still seems to be pretty unknown outside hardcore gaming) was done by texture packs (I've heard some have ripped Nintendo's VC half-translation and said even they used texture-replacement).
The rest only gets more obscure/"hardcore" from there. The Custom Robos, the Goemon board game, Super Robot Wars 64.
Now who's going to translate "Fire Electric Pen" (or whatever a good translation of the title would be), the N64 version of Irritating Stick?