At least for me (and the language-learning friends that I have spoken to), scheduling an exam for a language is not motivating at all. For instance, during high school, I took 4 years of French and I had plenty of exams (small quizzes weekly and bigger tests every month or so). The teacher graded us harshly, didn't encourage practical conversations in French, forced us to memorize verb conjugations again and again. I hated it, and for years after that, I thought that I had no natural talent for languages (that my brain wasn't designed for languages).
There are many other reasons why people learn a new language:
<ul><li>Because the language is useful for international commerce and business</li><li>Because they love how warm and friendly their people from that country are</li><li>Because they love the literature / history of that country</li><li>Because they love the way that the language sounds</li><li>Because they love the food from that country</li><li>Because their boyfriend/girlfriend speaks that language and they want to impress their boyfriend/girlfriend's parents</li></ul>
Any of these are stronger reasons than "I am going to schedule an exam to motivate me."
In the case of Chinese, for instance, you can try to show students how widely used Chinese is for business nowadays, how rich the literature / architecture / art of ancient China is, how delicious various types of Chinese food are, etc.
And for me personally, I am learning Italian right now because of how beautiful the language sounds, how friendly / sociable / fun Italians are, how delicious their food is, how warm / mild their climate is, and its deep impact on Western culture