Assessment methods are an essential part in language learning. Especially in educational contexts it is essential to provide learners with feedback, but not all assessment methods have a positive impact on the learners' motivation. Self-assessment is likely to play a key role in the assessment of foreign language proficiency. Language learning is closely linked with language attrition, a linguistic phenomenon where language skills deteriorate due to various instances. This thesis explores aspects of self-assessment and language attrition, taking a multilingual approach. The data used for the present thesis was gathered in the scope of the LAILA study (Linguistic Awareness in Language Attriters), a long-term project at the University of Innsbruck.