The oldest and most treasured books of the Jewish people have been the Torah and Tanakh (i.e. the Hebrew Bible) written almost entirely in Biblical Hebrew and widely used by Jews during their history. Jews maintained a belief that Hebrew was God's "language" as well (as it was the language God uses in the Torah itself), hence its name "lashon hakodesh" ("Holy language" or "tongue").
By the time of the destruction of the Second Temple, most Jews had shifted to speaking Aramaic, with a significant number in the large diaspora speaking Greek. As Jews emigrated to far-flung countries, and as the languages of the countries they were in changed, they often adopted the local languages, and thus came to speak a great variety of languages. During the early Middle Ages, Aramaic was the principal Jewish language. Later in the Middle Ages, most Jewish literary activity was carried out in Judæo-Arabic: Arabic written in the Hebrew alphabet; this is the language Maimonides wrote in. Hebrew itself remained in vigorous use for religious and official uses such as for all religious events.
As time passed, these Jewish dialects often became so different from the parent languages as to constitute new languages, typically with a heavy influx of Hebrew and Aramaic loanwords and other innovations within the language. Thus were formed a variety of languages specific to the Jewish community; perhaps the most notable of these are Yiddish in Europe (mainly from German) and Ladino (from Spanish), originally in al-Andalus but spreading to other locations, mainly around the Mediterranean, due to the 1492 expulsion of practicing Jews from Spain.
At the beginning of the nineteenth century, Yiddish was the main language of Jews in Eastern Europe (thus making it the language spoken by the majority of Jews in the world), while Ladino was widespread in the Maghreb, Greece, and Turkey; smaller groups in Europe spoke such languages as Judæo-Italian, Yevanic, or Karaim. The Jews of the Arab world spoke Judæo-Arabic varieties, while those of Iran spoke Dzhidi (Judæo-Persian); smaller groups spoke Judæo-Berber, Judæo-Tat or even, in Kurdistan, Judæo-Aramaic.
This broad picture was substantially modified by major historical shifts beginning in the late nineteenth century. The immigration of millions of European Jews to North America caused a dramatic increase in the number of Jewish English-speakers; colonialism in the Maghreb led most of its Jews to shift to French or Spanish; Hebrew was revived as a spoken language, giving it a substantially increased vocabulary and a simplified sound system; the Holocaust tragically and massively eradicated the vast majority of Yiddish- and German-speaking European Jews; and the Arab-Israeli conflict led many Jews to leave the Arab world for other countries (mainly Hebrew-speaking Israel and French-speaking France), whose languages they largely adopted.
Jews today speak a large variety of languages, typically adopting the languages of their countries of residence. The largest single language spoken by Jews is English, closely followed by Modern Hebrew.
Literary and theatrical expressions of Jewish culture may be in specifically Jewish languages such as Hebrew, Yiddish or Ladino, or it may be in the language of the surrounding cultures, such as English or German. Secular literature and theatre in Yiddish largely began in the 19th century and was in decline by the middle of the 20th century. Generally, whether a Jewish community will speak a Jewish or non-Jewish language as its main vehicle of discourse is dependent on how isolated or assimilated that community is. For example, the Jews in the shtetls of Poland and the Lower East Side of New York (during the early 20th century) spoke Yiddish at most times, while assimilated Jews in Germany during the 19th century or the United States today would or do speak German or English in general.