Does "foreign devil" mean "two devils"?

No, they have different meanings.

The term "foreign devil" is a collective term used by Chinese people for Japanese, European and American foreigners since the second half of the last century.

Erjiazi is the name given by the people in Northeast China to the Japanese soldiers from the Korean Peninsula who were sent to China during the Anti-Japanese War and the Korean political immigrants encouraged by Japan. The origin of Erjiizi is that the Japanese were called Japs at that time, and the Koreans/Koreans who illegally immigrated to China to work for the Japs and were responsible for controlling and killing the Chinese because of Japan's encouragement were called Erjiizi. It showed the Chinese people's disgust towards the people of the Korean Peninsula at that time.