The issue of key competences of teachers, including both matters of theory and teaching practice, belongs to most topical ones in scholarly discourses of both pedagogy and methodology of individual disciplines. The paper focuses on closer specification of the diagnostic and interventional competences of foreign language teachers within the scope of inclusive education, defining intervention as language advising during the learning process of a foreign language. Finally, the results of a research probe are presented which explored the diagnosis methods used by teachers of German and the way of language advising they provide to their pupils.