Playstation 2 mods?

The only instance I know of is where some people make translations of Japanese games. But to even play a JP game, you need your console hard modded, then you insert a file via usb to translate the game into English.

Man, how can I have missed this thread for an entire month?

I don't know much about modding on PS2, sadly, but I have seen it in some form. See, the PS2 pirates in Brazil were quite a creative bunch, so, if you had a hard modded PS2 to play pirated games, you could find a few gems being sold around. Most of them were GTA: San Andreas mods which replaced the characters and/or locations (I've seen Spiderman GTA, Dragonball GTA, GTA: Rio de Janeiro - which, in retrospect, makes this one seem almost like a documentary  ), but other famous ones were mods for football games (like Fifa and PES) which replaced the narrator, using any famous brazilian narrator instead; other mods replaced the teams and players, using obscure local teams. There were also a few translations.

MeleeMonk - It's as you said. Soft-modding is when you're only dealing with software, like changing the firmware of the system, which you may do with a SD Card, USB drive etc. By hard modded, I mean dealing with the hardware, that is, opening the system and modifying its components. I would be terrified of doing something like this to any console, but more experienced people do it for various reasons, like installing region switches (so you can play games from any region), outputting higher-quality video (like RGB or SCART) or, as is very common around here, to bypass the standard checks of the console so you can play pirated games or run emulators.

As I understand, some consoles give you a wide variety of stuff to do just by soft-modding them (I think the original XBOX is one of those; the PSP may be, too), but others, like the PS2, only open-up to more possibilities if you are brave enough to mess with its guts. As a curiosity, a lot of PS2s I found for sale around here in the 2000s were already modded, and that was seen as a bonus (as most people would mod them anyway). The problem is that Sony didn't have an oficial distributor in Brazil during the 2000s, so licensed games were really expensive (as they were all imports, so there was a lot of taxation going on). As a consequence, the pirated market thrived around here. I don't know more about it because, at the time, I was playing only on PC, as digital distribution made it possible to buy licensed games easier and for their real prices. But every one of my friends that had a PS2 also had a lot of pirated games for it - most of them didn't even have any licensed games.