When the Japanese soldiers confront Meldrick in the town square and, again, when the Japanese set an ambush on the road, they are wearing German "coal scuttle" helmets. In fact, contemporary photographs of the Japanese Army in China (e.g., during the Rape of Nanking) show Japanese soldiers with German army "coal scuttle" helmets, which, obviously, were purchased from Nazi Germany.
The Japanese soldiers shown are wearing German Stahlhelm helmets; however, they are wearing them backwards. Evidently the producers could not find any standard issue Japanese helmets and used the reversed German helmets. The Japanese did use this helmet, as they were superior to other helmets of the time, when they could get them from the beaten Chinese troops who had been issued these at the beginning of the war.
At the 14 minute mark when Gerald is getting a pedicure he says "Ouch!", but Gable's lip movement don't match him saying that word.