Is obedience due to a mother who refuses to speak Classical Arabic with her son in his daily life, even if he believes that the language of the Quran is more beautiful, impactful, and comprehensive than the colloquial dialect?

If a mother asks her son to speak in the vernacular and gets angry if he speaks in classical Arabic, he must obey her, because speaking in the vernacular is not a sin. However, he can try to gently persuade her of the virtue of speaking in classical Arabic.