Within the categorization of soft-pure and soft-applied disciplines, I never see a clear reference to “foreign language learning”. Perhaps this is due to the distinction between the five (or even more) linguistic skills: Reading, Writing, Listening, Speaking, and Translating. The outdated but still popular Biglan’s and Holland’s classifications did not take into account the typicality of areas such as communication in foreign languages (different from pure linguistics). Classifying multiple language skills according to concepts such as soft-pure or soft-applied could be tricky in some ways. Do you have any thoughts or relevant titles to share?