The view of the majority—and it is the sound position beyond any doubt—is that the Qur’an must not be rendered into another tongue. More than one scholar has even declared it impermissible to translate a single sūrah or anything that embodies the Qur’an’s miraculous inimitability.

Abū Ḥanīfah and his companions, however, disagreed about a person who is, in fact, able to recite in Arabic.

Concerning the obligatory remembrances (those parts of the prayer that are required but are not Qur’an), the question is whether someone who is incapable of Arabic and unable to learn it may recite them in translation. Within the Ḥanbalī school two views are reported. The opinion more consistent with Aḥmad’s own words is that no translation is allowed; this is also the stance of Mālik and Isḥāq. The second view permits translation and is held by Abū Yūsuf, Muḥammad ibn al-Ḥasan, and al-Shāfiʿī.

With regard to all other remembrances, the authoritative report from both sides is that they may not be translated; should one do so, his prayer is invalid. This is likewise the opinion of Mālik, Isḥāq, and some of the Shāfiʿīs. Al-Shāfiʿī himself explicitly stated that using a language other than Arabic is disliked but does not nullify the prayer, and some of our own jurists have allowed it when the worshipper cannot manage Arabic.

The ruling on speaking a foreign tongue in acts of worship—prayer, recitation, dhikr, the talbiyah, pronouncing the basmalah over a sacrifice—and in contracts and dissolutions, such as marriage, liʿān, and so forth, is thoroughly detailed in the legal works.

As for employing a foreign language unnecessarily in things like people’s names or the names of the months (in dates and the like), it is unquestionably forbidden when the speaker is ignorant of the meaning. When he does know the meaning, Aḥmad’s words still indicate dislike; he condemned the use of “Ādharmāh” and similar expressions even though their meanings are not in themselves unlawful.

I believe he was also asked about making supplication in the prayer in Persian; he disapproved and said, “A vile tongue!”