Thanks for your feedback!
Wokabulary is generally intended for learning single words and simple sentences. We know and appreciate that some users like to use it for learning longer sentences (or even paragraphs). And we try to make this work as well as possible but our primary goal is to optimize the interface for learning regular vocabulary lists.
Entering line breaks within words will generally not be supported and will be replaced with spaces. However, longer words (sentences) will be displayed with wrapping lines in the quiz.
For longer descriptions like grammar rules or sample sentences, you can always use the comment field, which not only support line breaks but even allows for Markdown formatting.