Since the end of 18 century, perhaps even earlier, most papers were probably published in German. And it kept this leading position until 1930s. I am not so sure about other sciences, but this was so in mathematics. Once I counted the PhD listed in the Math Genealogy project, by countries. Since the 18th century, the largest number (by far) came from German-speaking countries.

So it was "main" in terms of statistics. But certainly, English mathematicians wrote in English, French wrote in French, Italians wrote in Italian, and many (in all countries) wrote in Latin. So German was not "dominating" in the same sense as English is now. But in terms of numbers, one can safely state that the largest number of mathematical publications were in German, and the largest number of mathematicians lived in German-speaking countries.

Since the end of 18 century, perhaps even earlier, most papers were probably published in German. And it kept this leading position until 1930s. I am not so sure about other sciences, but this was so in mathematics. Once I counted the PhD listed in the Math Genealogy project, by countries. Since the 18th century, the largest number (by far) came from German-speaking countries.

So it was "main" in terms of statistics. But certainly, English mathematicians wrote in English, French wrote in French, Italians wrote in Italian, and many (in all countries) wrote in Latin. So German was not "dominating" in the same sense as English is now. But in terms of numbers, one can safely state that the largest number of mathematical publications were in German, and the largest number of mathematicians lived in German-speaking countries.

EDIT. For example, here is the 18th century distribution in Math Genealogy: Germany 317, Netherlands 122, England 24, France 14, Switzerland 8, Austria 7, Poland 1. Looks strange, of course. And I am not sure how to interpret this.

Since the end of 18 century, perhaps even earlier, most papers were probably published in German. And it kept this leading position until 1930s. I am not so sure about other sciences, but this was so in mathematics. Once I counted the PhD listed in the Math Genealogy project, by countries. Since the 18th century, majority of them came from German-speaking countries.

So it was "main" in terms of statistics. But certainly, English wrote in English, French wrote in French Italians wrote in Italian, and many wrote in Latin. So German was not "dominating" in the same sense as English is now. But in terms of numbers, one can safely state that most of mathematical publications were in German.

Since the end of 18 century, perhaps even earlier, most papers were probably published in German. And it kept this leading position until 1930s. I am not so sure about other sciences, but this was so in mathematics. Once I counted the PhD listed in the Math Genealogy project, by countries. Since the 18th century, the largest number (by far) came from German-speaking countries.

So it was "main" in terms of statistics. But certainly, English mathematicians wrote in English, French wrote in French, Italians wrote in Italian, and many (in all countries) wrote in Latin. So German was not "dominating" in the same sense as English is now. But in terms of numbers, one can safely state that the largest number of mathematical publications were in German, and the largest number of mathematicians lived in German-speaking countries.