I'm not sure about entire languages, but writing systems have been phased out relatively quickly. The Arabic script was changed to a Latin script in the Turkish language during the 1920s. Similarly, the Cyrillic script was introduced in Central Asia in the Soviet era. These were deliberate, political attempts to distance the countries from Islamic culture.

Well, if you look at the case of Israel, they revived the dead language of Hebrew, having all immigrants to Israel, speakers of many different languages, to give up their native languages to learn Hebrew. Because the immigrants were a minority, this did not have much impact on the native languages (such as German, French, Arabic, or English). However, this greatly impacted languages spoken only by Jews, like Yiddish and Ladino. Most Yiddish speakers were killed in the Holocaust and many others moved to Israel or the US and made the decision to speak only Hebrew or only English. Now, Yiddish is almost dead in the countries where it used to have millions of speakers, but it does live on in the populations of Hassidic Jews in Israel, the US, Canada, and a few other places.