Judeo-Spanish was the language of the Medieval Jews who lived in Spain, who are today called the Sephardic Jews, although the term does not necessarily mean a Spanish Jew any longer. It is a mixture of 15th century Spanish (the language of Cervantes) and Hebrew, although other languages also influenced it: Judeo-Spanish has been a minority language in contact with a variety of other languages (Malinowski). Ladino is the written form, and it is considered to be semi-sacred as it was used to directly translate the Hebrew and Aramaic texts. Therefore, the Judeo-Spanish language is seen as not only an important identity for the Sephardic community, but it also ties them to their beloved Torah and Mishnah. These and other factors may have contributed to the sustained use of Judeo-Spanish, as explained by Giles and Johnson:

members of subordinate groups who consider language to be an important dimension of their identity, identify strongly with their ethnic group, and make insecure comparisons with other groups are predisposed to act in terms of ethnic solidarity, define intergroup encounters in terms of ethnicity, and try to maintain their distinctive language features (Gudykunst and Ting-Toomey).

The Sephardic Jews who immigrated to other countries and maintained Judeo-Spanish probably had both high intergroup and high interpersonal salience-as in they considered Judeo-Spanish to be an important part of their identity, and strongly identified with their ethnic group. Their religious belief of being "set apart" by God as His holy people was a large part of this community’s worldview and self-perception. In addition, the impact of being semi-forcibly expelled from Spain, and later the Holocaust must have increased group cohesiveness as a natural psychosociological response, and decreased the desire to conform to society (Gudykunst and Ting-Toomey 320).

On a societal level, the pluralistic Turkish commercial centers (which were home to large Sephardic communities) during Ottoman rule allowed for minority practices and beliefs, so that Jews existed often in business and always in private life... as a millet, living in their separate quarters, establishing and staffing their own schools, observing their own customs and ordinances (Malinowski). They were not required to learn Turkish, and according to Malinowski, Judeo-Spanish came, inevitably, to be perceived as an "essential determinant of group identity and group unity." In fact, this group identity was demonstrated in a very real way when listening to the narratives of people:

The sense of group unity and continuity received its perhaps most telling expression in the informants' habit of using the first-person plural- verbs, or course, in the past tense- when narrating the events surrounding the expulsion. For example, Estuvimos en Espanya, Mos fuimos de la Espanya, Mos aresibyo aki- 'We were in Spain', 'We left Spain', 'We were welcomed here.'(ibid)

Some of the distinguishing traits of Judeo-Spanish from the Standard Castilian of the 15th century include the pronunciation of j as "zh" or "sh" so that the Spanish word dejar was pronounced /deshar/. Often words have an added n and the r is reversed with another letter, so mucho is spelled and pronounced muncho, gordo as godro and pobre as prove. In addition many words were borrowed from Arabic, and Arabic sounds were borrowed to form words such as Alhát which is Arabic for the first day. Interestingly, due to the importance of the Oneness of God, the Spanish word for God (Dios) was made non-plural and the Hebrew El was added to it: El Dio. The z remained in some words and therefore mesa was pronounced "meza" (/meΘə/).
          Finally, Judeo-Spanish, with its historical mix of Hebrew, 15th century Spanish, Aramaic, French, and other languages that layered over it over time, is still used today in various Sephardic communities around the world. While the number of speakers has diminished- partly from the systematic destruction of European Jews, and also due to the acculturation of some Jews- there are still communities keeping up the tradition. The language has become part of their lives, as it is tightly interwoven with the faith of many Jews. Malinowski interviewed dozens of Sephardic Jews of various ages and found that both in the past and even now,

Language and religion... still appear to be intimately related in the self- and group-perceptions of the Turkish Sephardim... it was... regularly and promptly assumed that anyone who spoke Spanish was in fact Jewish.

Works Cited:

Gudykunst, William and Stella Ting-Toomey. "Ethnic Identity, Language and Communication Breakdowns."
Handbook of Language and Social Psychology. Ed: H. Giles and W.P. Robinson.
John Wiley & Sons Ltd., 1990

Malinowski, Arlene. "A report on the status of Judeo-Spanish in Turkey."
International Journal of the Sociology of Language. 37 (1982) pp. 7-23.