What the title says.
Is there a program that can do it, or do I have to use one of those ugly hex editors?
You can go the "Sin & Punishment" way:
1. Find a game that relies solely on textures to represent the ingame text
2. Dump textures from a rom with the help of a special graphical plug-in for a N64 emu
3. Edit\\Replace the dumped textures with translated ones
4. ? ? ? ? ?
5. Profit!
(That's how it goes, right?)
But I don't think there are many games like that.