Historical accuracy?

Historically speaking, this movie takes place in one of the most complicated eras in East Asia's modern history. One can attribute it to the colonial-era Middle east. Due to Japanese occupation of Manchuria (northeast China) and Korea (and the infrastructure and perceived economic opportunity), the entire region became the melting pot of East Asia, which is why you see everything from Han Chinese, ethnic Manchurians, Mongolians, Russians, West Asians, Koreans and Japanese (not to mention some westerners i.e. the train conductor) all gathered in a single region, something that is not very common even today. It may be difficult to decipher to a non-native speaker, but I counted 3 East Asian languages with at least 5 separate dialects spoken in the movie.

The lawlessness visible is most likely attributed to the state of chaos after the disbanding of local governments by the Japanese occupation, and the traditional tribal nature of the denizens of the Gobi Desert.

In terms of equipment and weaponry, this area would probably have have had some access to American and British firearms due to it's role as the cosmopolitan center of East Asia, but not to the degree portrayed in the film. While the Smith and Wessons, Colts, Walthers, Lugers and Webleys were period-accurate, most guns in the area would have been Nambu pistols (official Japanese sidearm), Mauser c96's (used widely by the Chinese), or russian made Nagant revolvers. Western firearms would have been incredibly valuable and somewhat rare in 1930's East Asia (which, on second thought is why they are carried mainly by crime bosses and successful bandits). The western-style revolvers were likely chosen because they were period-accurate and they looked cooler and paid more of a homage to the spaghetti-western genre.

Clothing-wise, the film probably took some creative liberty here, but its not like anything is glaringly anachronistic. Like I mentioned above, many of the film's characters would have come into contact with some westerners and very realistically could have adopted the dress style. In addition, keep in mind that at this point in time, the entire area is part of Japan, and the Japanese had adopted a western-dress since the late 1800's. While I doubt there were many East Asians dressing like American cowboys, I do think the film did an excellent job in portraying the look and feel of 1930's Manchuria - you get the full mix of western, Chinese, Manchurian, Korean and military Japanese clothing.

Hope that helps!