May one pray in another language?
The Shulchan Aruch (O.H. 101:4), basing himself on the Rosh (Berachot, ch. 2), writes that one may pray in any language that one understands. Rabbi Baruch Toledano (Kitzur Shulhan Aruch, 90:6) writes that women and people that did not know Hebrew could pray in Arabic or any other language they knew. On the other hand, the Hatam Sofer (§ 84) comments that the Shulchan Aruch’s intention is that one may do so on an intermittent basis, not consistently, and that it is inappropriate to recite the entire prayer in a foreign language. Historically speaking, the Hatam Sofer’s opinion was also in response to the Reform movement, who sought to translate the prayer into German and also to remove any references to Zion.
In previous generations, the Hebrew language was understood mostly by a scholarly elite and therefore the prayer was not easily accessible to all. Nowadays, however, Hebrew reading and comprehension are immeasurably more accessible to the average person. Furthermore, there is a wealth of translated and transliterated Siddurim available such that praying in Hebrew is much easier. Siddurim nowadays are, for the most part, punctuated with Nekudot, which also makes reading even easier than non-punctuated text. Additionally, the Kaf HaHaim (K.H., O.H. 101:16) says that the Hebrew language is replete with Kabbalistic power that cannot be mimicked by another language. Thus, although permitted according to the letter of the law, it is inappropriate for one who is not yet literate in Hebrew to remain so long term and to pray in one’s native language.
That being said, there are circumstances in which one cannot at the moment pray in Hebrew, such as a convert or a Ba’al Teshuva. In such a case, one should pray in whatever language one knows rather than skip the prayer altogether. Certainly, part of such a person’s Jewish learning should include mastery of the Hebrew language.
It should be noted that this Halach applies in the strictest sense to the Amida and the established prayers that accompany it. Regarding different supplications, Piyutim and the like, the Kaf HaHaim (ibid:17) says that there is much more leniency in reciting them in different languages. Examples of these include the Bendigamos hymn before Birkat Hamazon that is recited by Spanish Jewry or En Kelokenu that is sung in Arabic by Moroccan Jews.
Summary: Strictly speaking, one may pray in any language. Practically speaking, however, one should only do so if circumstances necessitate it and should strive to learn and pray in Hebrew. Portions that are not central to the prayer may be recited in different languages.