Title of a latin dissertation

These two phrases seem clear:
De principiis --> concerning the principles
linguae condendae --> of a language to be built

but the phrase in fundamentum literally means "into the foundation"
and I am not sure how that fits. Perhaps he means the fundamental
principles of a language to be built, that is, the basis of building
a language. But I am not certain.

Thank you for your help, George!

Perhaps it means:
About the principles of the origin of languages.
Sorry about my English!

I like that.