Can I make dua in English during prayer?

Outside the prayer: no problem at all

Allah understands every language. After the salam, while sitting on your prayer mat, in the car, or in bed at night, you can ask for anything in English, in your own words. Allah says, "Call upon Me; I will respond to you" (Quran 40:60). See Can I make dua in English?

Inside the prayer: what scholars say

The prayer has a set structure in Arabic: takbir, al-Fatiha, the dhikr in bowing and sujood, and the tashahhud. Those fixed parts are said in Arabic by all schools. The question is only about extra personal duas, for example in sujood or at the end of the tashahhud, where the Prophet ﷺ said: "Then select the invocation you like best and recite it" (Sahih al-Bukhari 835).

• Hanafi and Hanbali schools: generally say duas inside the prayer should be in Arabic, and many of their scholars consider a non-Arabic dua there not allowed.
• Shafi'i school: someone who can't yet say a dua in Arabic may say it in their own language; someone who can is asked to use Arabic.
• Maliki school: many Maliki scholars also discourage non-Arabic duas inside the prayer, while some show more flexibility for those who can't manage Arabic.

Because of this difference, many teachers advise converts to stay on the safe side in the obligatory prayers, and not to worry that their prayer is "less" because their Arabic is basic.

A practical middle path

• Learn 2-3 short Arabic duas: for example "Allahumma-ghfir li" (O Allah! Forgive me), which the Prophet ﷺ said often in bowing and prostration (Sahih al-Bukhari 817), or "Rabbana atina fid-dunya hasanah wa fil-akhirati hasanah wa qina 'adhaban-nar".
• Know their meaning: when you understand what you say, your Arabic dua becomes just as heartfelt.
• Use English straight after salam: stay seated a minute and ask for everything you need in your own words.
• Use voluntary prayers: if your school allows it, your sunnah or night prayers are a gentler place to start.

What if I already did it?

If you made duas in English inside your prayers because you didn't know about this difference, don't panic. You were following what you knew, and many scholars allow it for people in your situation. Simply move toward Arabic duas from now on, step by step. For more on duas in sujood, see Can I make dua during sujood?