Whether or not this man trumped a tweet correctly or not is left to judge for the reader:
While all this activity was going on, increasing numbers of French children and adults began learning German. The Berlitz language school increased its enrollments from 939 adult students of German in 1939, to 7,920 in 1941; the German Institute in Paris from a few hundreds in the 1930s, to 15,000 by 1942, mostly taught by French instructors. Altogether, some 30,000 students took courses at the German Institute; the majority were adult members of the urban middle class and the liberal professions, with a total of about 100,000 French people learning German during the Occupation.
This in turn reflected the accommodation of the intellectual and academic elites. Institutions of higher education, ranging from the Collège de France to practically all universities, rapidly and voluntarily purged themselves of their Jewish members, without any registered public protests by the professors. The prominent historian Lucien Febvre demanded the resignation of Marc Bloch, the Jewish coeditor and co- founder of their journal Annales, so as to save it from being banned. While Bloch joined the Resistance and was executed by the Germans, Febvre continued to edit the journal –– which in no way promoted resistance –– from the safety of his country house. Similarly, such respectable French publishers as Gallimard purged their lists of Jewish authors and turned to publishing texts by German racial ideologues and French collaborators. Nor did many renown French writers desist from having their works published during the Occupation, including Louis Aragon, Georges Bataille, Simone de Beauvoir, Maurice Blanchot, Albert Camus, Paul Claudel, Marguerite Duras, Paul Éluard, François Mauriac, Jean Paulhan, Romain Rolland, Jean-Paul Sartre, and Paul Valéry. Marcel Aymé wrote for the fascist antisemitic journal Je suis partout, Mauriac contributed to the collaborationist Nouvelle Revue Française, Camus cut out a chapter on Franz Kafka from Le Mythe de Sisyphe to have it published in 1942, Antoine de Saint-Exupéry paid a quasi-official visit to Germany to promote the translations of his books there, and Aragon excised references to Heinrich Heine and the Dreyfus Affair from his writings to facilitate their publication in Germany. Other artists followed suit. Jean Cocteau expressed admiration for Hitler, Abel Gance made a friendly visit to wartime Germany, and Pierre Fournier gave concerts in the Reich. That some of these men and women eventually ended up in the Resistance only highlights the moral confusion and the depth of accommodation that characterized the French intelligentsia in the first years of the Occupation.
Omer Bartov: "Mirrors of Destruction: War, Genocide, and Modern Identity", Oxford University Press: Oxford, New York, 2000, p 65.
Bartov quotes this number from Philippe Burrin: "France under the Germans, Collaboration and Compromise, New Press: New York, 1996., p299–305. Repeatedly:
A striking example of French accommodation was the expansion of German
language instruction. The numbers of French schoolchildren learning German rose dramatically, especially in Paris. The Berlitz language school had 939 adult students of German in 1939, but 7,920 in 1941. Some 30,000 people took courses at the German Institute, most of them adult members of the urban middle class and the liberal professions. A total of about 100,000 French people were learning German during the occupation, their numbers reaching a peak in 1942 and then dropping as the prospects of a German victory diminished.
Intellectual and academic elites were also very much part of this process.
Review: The Proof of Ignominy: Vichy France's Past and Presence, Contemporary European History, Vol. 7, No. 1 (Mar., 1998), pp. 107-131
An assessment that gives some numbers, but apparently implies very little:
Burrin’s concept of accommodation uses broad, contextual analysis to evaluate decisions made by various social groups including the Catholic Church, captains of industry, intellectuals, and regular French men and women who struggled to survive during the Occupation. Did French men and women who served a German cliente`le, manufactured products for the German war effort, or simply learned to speak German sympathize with the ideological goals of the Nazi regime, support resistance efforts, or just try to make some easy money? Without passing judgement, Burrin suggests that many people balanced personal ideals against the necessities of life and accommodated some German demands without necessarily endorsing Nazi goals.
Thomas J. Laub: "After The Fall. German Policy
In Occupied France, 1940 – 1944", Oxford University Press: Oxford, New York, 2010, p8.
So of course: when one army invades a country with a different language, there is a certain incentive to learn the language of the invader, if you do not already know it. Almost equally, the invading army will have to up their language skills. Therefore, the original tweet would have to be amended that "until the time the Americans came along, the Germans were learning French in Paris"?
When the Americans went to Vietnam one side started to learn French and Vietnamese, the other started to add English to their repertoire as well. When the German army invaded Russia, they had interpreters with them to translate from and into Russian. When the Russians approached Berlin they had bi-lingual people in company. When the French occupied parts of Germany under Napoleon the rate of learning French in Germany increased. This is always going both ways. Contact necessitates communication. For that you need a common ground and that is language.
Why this stirs any controversy seems quite beyond reasonable thinking.