We describe work carried out in the context of a project whose goal is to develop a web-enabled serious game, designed to help German-speaking beginner students of English improve their generative and auditory competence. The game, which is currently undergoing a first round of formal user testing, is intended as a self-study adjunct to normal classroom instruction. It was developed in collaboration with a secondary school teacher, with the content taken from a textbook commonly used in German-speaking Switzerland, and offers a short course of 8 interactive lessons using a combined vocabulary of about 450 words. A lesson is structured as a short prompted dialogue between the student and the machine, where the student is encouraged to use simple language in practical contexts like booking a hotel room, buying clothes, or ordering a meal in a restaurant. We present an overview of the architecture, which is designed to balance three main considerations: it should support coherent grammatical responses and reasonably interesting dialogues, but also allow course content to be constructed by personnel who do not necessarily have a computer science background. We use as an example a new strategy we have recently developed, where the central idea is to add further dialogue paths to the scripts, graded by their degree of “cooperativeness”. The system starts with a simple cooperative interaction, and opens up increasingly "uncooperative" dialogue paths as the student gains familiarity with the game.