My source is mishna brura 307.5 which says to say shabbas shalom, “or as we say in mundane language” (ie yiddish, the language he spoke) Shabsa Tava (“gut shabbes”)
So he spoke yidisha and called it a lashon chol. Others referred to it as lashon ashkenaz, the Germanic tongue. Teitch literally means deitch, the Germanic language.