If we accept it as a given that the native tongues of all ethnic peoples are grammatical, the question that unfolds from this is:
How does the language attain its sentient semantics by which the person can live his life to attain his goals and ambitions, wants and desires, needs and greeds and the cover for his worries, anxieties and the cover for his fears?
Clearly, the grammar of the spoken tongue, in and of itself, cannot do this.