Joseph, Rav Yosef Chaim Sonenfeld ZT”L actually DISAGREES with you re: Modern Hebrew. I read in the Yated or Hamodia (by Rav Sonenfeld’s Yahrtzeit) that after Ben-Yehuda died, some of his follwers came to him and asked him if this was a case of “binfol resha’im, rina”. He responded that we don’t know what sechar Ben Yehuda has in shomayim for getting people to speak Loshon Hakodesh, even if it’s corrupted. Ein Hashem Mekapeach sechar kol berya. Furthermore, he hopes Ben Yehuda is going to shomayim. While he fought against Ivrit, due to its harmful influence at the time, the familiarity of Israelis with Lashon Hakodesh helps them do teshuva faster, and helps chareidim learn more Torah. Furthermore, in Israel, Ivrit is the language of communication in most of the Chareidi sector. The ideology of Ivrit is gone, as the Chazon Ish said a while ago.
We also don’t know if the Chasam Sofer applies now. He was writing at a time when Jews were throwing off the yoke and leaving the shtetl, and throwing off Yiddish was part of the prikas ol. Today, English is the spoken language the way German was 500 years ago. It’s for the same reason that Rav Shach’s statement is no longer relevant, which is why we are left with the 3 big Litvishe poskim (Mishna Brurah, Aruch Hashulchan, Igros Moshe cited above in O”C 5) that Yiddish is a lashon chol, and the Jews shouldn’t have adopted the goyishe German names we now know as Yiddish names, except it’s too late to protest.
If you have the time to learn Yiddish, get a real mitzvah and learn Torah or say Tehillim. You are getting an actual mitzvah.