There is a solid argument that it's not. These are rules for a language. And there obviously is NO creativity involved, it's just a compilation of facts about the language. Of course it's work to produce a dictionary, but that's not a criterion for copyrightability.
IANAL, but according to my understanding of swiss, german and US-law, I'd say you're on pretty good ground by assuming its not copyrightable. Maybe ;)
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