Within the study of language in society, new sociolinguistic notions are increasingly gaining ground, e.g. the notion of polylanguaging. Polylanguaging is defined as "the phenomenon that speakers employ linguistic resources at their disposal which are associated with different 'languages,' including the cases in which the speakers know only few features associated with a given 'language.'" This paper aims to investigate foreign language learners' written language use with a view to the notion of polylanguaging. The participants of the study are 49 Swiss university beginner learners of Danish as a foreign language in Switzerland. The data consist of written learning journals about the participants' experiences with learning Danish through a year and a half. The data collection method permits a direct comparison of the participants' language ideologies with their language use. The paper argues that learner language, understood here as language produced by learners in an institutional setting, is closely related to polylanguaging. The participants draw on several languages when producing learning journals. However, university students and the participants of studies on polylanguaging do generally not use linguistic features associated with different languages for the same reasons.