What language is the oath in?

The Oath of Allegiance is administered in English. The text of the oath is set out in section 337 of the Immigration and Nationality Act (8 U.S.C. section 1448) and is also published in 8 CFR section 337.1. The standard oath reads: I hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state, or sovereignty, of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I will bear arms on behalf of the United States when required by the law; that I will perform noncombatant service in the Armed Forces of the United States when required by the law; that I will perform work of national importance under civilian direction when required by the law; and that I take this obligation freely, without any mental reservation or purpose of evasion; so help me God.

The phrase so help me God is optional, and applicants who object on religious or moral grounds may omit it and substitute solemnly affirm for swear or oath. Applicants who, by reason of religious training and belief, are conscientiously opposed to bearing arms or to performing noncombatant military service may apply to take a modified oath omitting the corresponding clauses; the modified oath is administered if USCIS approves the applicant's request supported by evidence of the applicant's religious or conscientious belief.

The oath is recited collectively at the naturalization ceremony, with all candidates standing, raising their right hand, and repeating the words after the presiding officer (a USCIS officer or, in judicial naturalization ceremonies, a federal or state judge). Although the recitation is in English, USCIS provides a written translation of the oath in many languages on the agency website, and applicants who used an interpreter throughout the interview will typically have the oath explained to them in advance so that they can recite it accurately. The oath ceremony itself, including the recitation, is the moment at which the applicant officially becomes a U.S. citizen.