were there any mods made for srb2 back in the demo 1\2 days?
Of course. People could make levels and stuff then, too.
You're probably looking for a more detailed answer, though..
*) I have a diving wad from Sept. 2001
*) Beach.wad from July 2001 (is this an old map of Mystic's?)
*) Blaze.wad from March 2001, character skin
*) CHAO.WAD, a character skin made by Rlan, June 2001
*) CINO.WAD, a character recolor of Sonic Retro member Cinossu that he made in 2001. :)
*) Quite possibly the first version of Mystic's Jade Coast Zone, July 2001
This is obviously an incomplete list and just for example. These are ones that I've hung on to. Maybe I have more, who knows, I don't have my old stuff organized well.
Everywhere? The only japanese symbol I've seen so far inside SRB2 was the old Score Emblem. I've read that there may be something of the sort in Frost Columns Zone, but I don't know for sure.
I'm not a fan of the easternization of the game. Sonikku hid some japanese in a level or two, but I tolerated it because a) it was hidden and b) hey, it's Sonikku.
English is kind of a 'lowest common denominator' language.. it's bad enough for a foreigner to have to know English to play, it's very unfair to also expect any knowledge of Japanese.