  This paper presents the development of an AI-based language learning platform
Revita. It is a freely available intelligent online tutor, developed to support
learners of multiple languages, from low-intermediate to advanced levels. It
has been in pilot use by hundreds of students at several universities, whose
feedback and needs are shaping the development. One of the main emerging
features of Revita is the introduction of a system of linguistic constructs as
the representation of domain knowledge. The system of constructs is developed
in close collaboration with experts in language teaching. Constructs define the
types of exercises, the content of the feedback, and enable the detailed
modeling and evaluation of learning progress.
