If one is raised with the mindset that Yiddish is the only proper language for a Jew to speak conversationally, then there is really no changing that person’s mind. Before the Yiddish language was created, I suspect Jews spoke to each other nonetheless. And as I do not speak Yiddish, I will stick to the two languages in which I am fluent, English and Ivrit, and use them both.
Hashem’s intention was for ALL mankind to speak ONLY Ivrit. It was not until the Migdal Bavel incident that other languages were created by Him. I will presume that prior to that all mankind had many topics under discussion besides Torah, in the course of a day, including topics that made them chuckle. So I will likewise presume Hashem was apparently ok with Ivrit being spoken when discussing the weather, or else He would have created those second languages much sooner and instructed Adam and Chava NOT to speak Ivrit when say, tending to the animals or finding something to be humorous.
Yiddish had a vital place in Europe for a long time and should be honored for that reason. But to say it is more or even as holy as the language that MOST Jews speak today, is to be a little out of touch with reality. What Yiddish does today is the exact opposite of what it did before. Instead of INCLUDING vast numbers of Jews, it excludes most of us who no longer speak it.