The Nazis certainly had a programme whereby they sent anthropologists and linguists to the US to learn Native American languages, partly in response to the successful use of Choctaw code talkers by the US Army on the Western Front, which is why the US didn't use the Navajo in Europe, and the Germans never cracked the codes used by Comanche or Cree code talkers in Europe in the Second World War either. The Japanese did capture a Navajo soldier, Joe Kieyoomia, and tried to crack the code, but as he never took part in the programme he could not interpret the messages. Neither of the major Axis powers recruited native Navajo speakers it seems, but they did try.