Chazal tell us that one of the reasons Bnei Yisroel merited to be taken out of Mitzrayim was that they did not change their language. What, however, was that language? The Otzar Pilaos HaTorah discusses this at length and brings various opinions.
The Maharsha in Megila 3a says that in Mitzrayim Bnei Yisroel spoke Aramaic, their mother tongue that was their inheritance from their youth spent in the home of their grandfather Lavan HaArami. Yet in Sanhedrin 21b the Maharsha says that they spoke Lashon HaKodesh and not Aramaic. Rav Yaakov Emden explains that Avraham spoke two languages, Lashon Kodesh when he spoke Devarim Shel Kedusha, and Aramaic for any mundane conversation that he needed to have. This dichotomy was followed by Bnei Yisroel in Mitztrayim, who did not change this custom and did not change their language to Egyptian. This would explain the Maharsha.
The Meor VaShemesh says that Bnei Yisroel did speak Egyptian in Mitzrayim, however they did not speak the foul language of the Mitzrim, and thus kept their language Holy.
The Chasam Sofer (Parshas Naso) says that when Chazal say "Devarim Hayotzim Min HaLev Nichanasim El HaLev", words that emanate from the heart have the ability to penetrate the heart, it refers only to Lashon HaKodesh. No other language has that ability to penetrate a heart. Nevertheless the Lev Ivri (on the Tzava'a of the Chasam Sofer) writes that this applies to Yiddish or any other language adopted specifically by the Jews. He adds that although the Arizal would not speak Divrei Chol on Shabbos, he would speak Divrei Torah in the adopted language of his time.
To corroborate this, the Chasam Sofer himself in his Drashos praises the Jews of Russia and Poland whom hundreds of years after being expelled from Germany, still spoke Yiddish and did not pick up the local language.
From these opinions we see that there are three aspects of language. First the intrinsic kedusha itself. Second, as a tool to keep ourselves separate and apart from the other nations. Third to keep it clean. May we be zoche for Chazal to say on us one day,that we brought the Geula because we did not change our language!