With the existence of fan translators capable in the language, we have more accurate translations of the original Japanese scripts of games like Sonic Adventure and Sonic Adventure 2. One thing that viewers were quick to notice, however, was that the Japanese rendition of Sonic seemed more polite while the American version of Sonic seemed more rude.
I'm not an expert on Japan or its culture and language (so take everything I say here with a grain of salt and feel free to correct me if I'm wrong), but from my passing knowledge I think what a lot of people are missing is that Japanese culture has a different threshold for what constitutes as informal or rude, and that the way informality or formality is expressed in Japanese culture is oftentimes something that cannot be 1-to-1 translated without losing its meaning.
For example, Japanese has different ways of saying "you". One of these is "omae", which is a rough informal "you" generally used by people being rude or looking for a scrap. Sonic uses "omae" fairly frequently, and if Sonic does this more frequently than other characters, it'd definitely indicate him being a bit rougher-around-the-edges. (Unfortunately I don't have the ability to fully analyze Sonic's lines atm).
The problem that arises from this is that there's no real English equivalent to an informal "you" aside from inflection. But translated literally, "omae" is still just "you", which would perhaps lack the same impact that "omae" has in a Japanese context even with a rude inflection. The other problem that arises is that, due to how formality seems to be stressed in Japanese culture, their threshold for rudeness is possibly much lower than America's threshold... which would also explain how the Japanese stereotype for Americans tends to be very American, because from their view Americans kinda just do whatever the heck they want (the dots begin to connect when you realize that much of Sonic is a result of Japanese interpretation of American culture). But my point being is that while Sonic saying "omae" and other similar word choice may be enough to cut it to make him rude, scrappy, and defiant in Japan, it simply wouldn't be enough to convey nearly the same degree of rudeness in the west if translated literally. So, Sonic's rudeness has to be upped an ante in America to convey that same idea.
Theoretically they'd still be the same level of rudeness, just adapted to each culture. Because what may not be rude in one culture could be very rude in another. Take this all with a grain of salt however, as again I'm an expert in the least. But this is why localization to SOME extent is necessary, because a literal translation can't always convey the original intent. Not that the Sonic localizations have always been the best. There have been a number of poor localization decisions or mistakes in Sonic's history, and much of the Classic era's localization was downright awful. But used properly, localization is an excellent tool for conveying the same meaning properly to an audience of a different culture.
That maaay have been a bit of a tangent, oop. I guess I'll provide another example really quick for the heck of it. Japan uses honorifics, suffixes appended to the end of surnames that are applied depending on context and relationship between the parties involved. For example, "-san" is used as a sign of respect between equals in both informal and formal contexts. "-sama" is used to refer to a superior, but someone addressing themselves as "-sama" shows that they have a very high (if not outright overly self-important) view of themselves. Eggman often uses "-sama" when referring to himself, demonstrating his ego and sense of greatness. It's another step of showing just how egotistical he is, and serves as an excellent contrast to Sonic who doesn't use any honorifics to refer to himself.
It's still possible that Sonic is nicer in the Japanese version than the American one, even when taking the cultural context into account, but that would definitely require an in-depth knowledge of both cultures to make that call. For example, Sonic asks Knuckles if he's "simple-minded" in the Japanese version of SA1, while the American version Sonic outright says "Way to go Knucklehead!". From an American perspective, one is definitley ruder than the other, but would Sonic asking Knuckles if he's simple-minded be just as rude in Japan as Sonic calling Knuckles a knucklehead in America? I'm not sure.
Overall this is just the tip of the iceberg as I lack the knowledge to really in-depth analyze the Japanese script, but I do think that people may be pegging Japanese Sonic as more polite than he actually is, at least in some cases.
Anywho, that was my obligatory random Sonic analysis post. I'll see you all on the flipside. XP