Upvote:4
Both Japan and China had more pressing issues than a civil war half the world away. Note that long distance travel was harder and more expensive then.
wiki:
Some Chinese joined the Brigades, and the majority of them eventually returned to China, while some went to prison or French refugee camps, and a handful remained in Spain
Benton, Gregor; Pieke, Frank N. (1998). The Chinese in Europe p. 215
After being spurned in Paris, Japan took little notice of European development.