''Dirac deeply influenced Tomonaga, and through Tomonaga he had a pervasive influence on an entire generation of Japanese physicists. During the summer of 1935, Nishina, Kobayasi, Tamaki, and Tomonaga – the theoretical group of the Nishina Laboratory – 'devoted' themselves to translating Dirac's 'famous textbook of the quantum theory' into Japanese.
We three rented a small villa at Karuizawa, a famous summer resort of Japan where Nishina stayed with his family. As soon as we started work, we found how difficult it was to translate English into Japanese which has a completely different sentence structure. The work of translation was really heavy labour, and sometimes we became so tired that we all became bad humoured and disputes often arose over trifling matters. But we made it a rule to take a rest on Sundays and on finishing every chapter, to make excursions to neighboring hills and meadows. The beautiful landscapes and refreshing air were so effective that we all recovered our good humour and we were able to continue our hard work. We believe that the Japanese edition of Dirac's book has been and will continue to be appreciated by many physics students of our country. (Tomonaga 1976, pp. 466-467.)''
In Schweber, QED and The Men Who Made It: Dyson, Feynman, Schwinger, and Tomonaga, pp. 255-256.