Clauses? Like conditions for your spells? Is it more like you put the magic in the object and the object does the spell if you need them for the spell and magic? That makes sense. About the sleep remedy and tea.
Theoretically? Any language. But there are ancient languages a lot of spells are in, but not everyone speaks the same language, so some spells can be done in other languages. I don't know all the rules, but that's probably why I'm still in school. But witches from different parts of the world had to come up with some way to use their magic before mass communication.