[deleted]
Having taught English (briefly) at a Japanese medical school, I can say that German wasn't at all common among the Japanese medical students I was working with. What _is_ common is a German influence on academic and scientific vocabulary, dating back to the Meiji era, when Japanese perceived Germany, newly victorious in the Franco-Prussian War, to be the most advanced nation.
So at that time, and up to the Second World War, you have a substantial number of Germans teaching in Japan, and Japanese studying from German texts. Note Japanese high school boys' collarless jacket uniform ("gakuran" 学ラン), modeled on Prussian"cadets" and the waffenrock. Similarly, you can note German influence in domains like politics and finance-- that's the reason the Japanese settled on the term "Diet" for their legislature, and not "Parliament". The Japanese saw a model for their 1889 Constitution in Wilhelmine Germany. You'll hear a lot of German loan words in academic terms-- a "seminar" is a zemi, and the Japanese didn't just pick up the word, they modeled their graduate education on German university seminars.
In the "Charter Oath" of 1868, the Japanese declared their policy:
Wisdom and knowledge shall be sought all over the world in order to establish firmly the foundations of the Empire
. . . and they meant it. "Global best practices" wasn't just a bullet point on consultant's powerpoint-- it was Imperial policy, consecrated by the Emperor in a dramatic ceremony; one part ancient Yamato, one part McKinsey.
The Japanese were empirical and open minded in their choice of foreign models-- although the Army admired the French (up to 1870), and the Germans thereafter, the Navy modeled itself on the British Navy. This was one of the sources of the tension between the Imperial Navy and Army-- they were two very different military cultures to start with, and their training took them farther apart. So, for example, the famous General Nogi (of Port Arthur fame), studied in Germany, while Admiral Togo (of Tsushima) studied in Britain.
In the same fashion, the Japanese had an inquiry to see "whose medical system should we adopt"-- with the contenders being Germany and Britain:
In March 1870 the Japanese government officially adopted German medicine; the runner-up was British medicine. The first German professors arrived in Tokyo in September 1871, and for the next two decades they dominated the school that was to become the prestigious Faculty of Medicine of Tokyo Imperial University. All Japanese medical faculties adopted the philosophy and practices of German medical schools, and continued to do so until the middle of the twentieth century; the German influence is readily manifest even today [meaning 1979].
Today, though, a medical student wants to be able to read journals and textbooks, which are overwhelmingly in English; there's much less published in German, and while I encountered one or two older professors who read German, none of the students I was working with in 1986 did.
Finally, remember that specialized technical vocabularies are very persistent, but that doesn't signify any real capacity in the language- English speaking lawyers and physicians routinely use a lot of Latin and Anglo-Norman Law French vocabulary in their professional practice, without actually speaking the language at all.
Sources:
THE ADOPTION OF GERMAN MEDICINE IN JAPAN: THE DECISION AND THE BEGINNING
The Imperial Oath of April 1868: Ritual, Politics, and Power in the Restoration
Europe versus Asia: foreign language education other than English in Japan's higher education
Japan's Imperial Diet Building: Debate over Construction of a National Identity
what evidence do you have to backup your assertion that German is a common language among Japanese doctors? This was not my experience from living in Japan.