I have no idea if it's ever been popular, but German is a language most people learn in school as a second foreign language after English. In 7th grade we can choose what language we want to study. In many schools there are only teachers in German and French, but others may have many different languages, like Spanish or Japanese.
This is what is said on wikipedia:
German was introduced in the Swedish school in 1807, like other modern foreign languages after French (and Latin). In 1859 French was replaced as the first foreign language in all the former secondary educations. On 10 March 1939 the Government of Sweden decided to start a trial with English as the first foreign language in a number of schools, and English was introduced as a first foreign language throughout Sweden August 26, 1946.