Funkelregen doesn't mean "Rain of Stars"
Funkel = Spark / Sparkle
Regen = Rain
So it would be "Rain of Sparkles"'
Edit:
Since it is later mentioned, you can ignore the post above.
Yes, you are right. I only mentioned it because I am from Germany and noticed this. Since the MC later explains how he means it, I added the edit sentence later.
I only have thought about how to translate it in a kind of literal sense and not in the way someone could express it without losing the original meaning of the German word.