Short answer
Yes. Outside salah you may make dua in English or any language: Allah knows every language and every heart. The duas of the Quran and Sunnah in Arabic carry extra blessing, so learn some of them too. Inside salah the Hanafi school keeps dua to Arabic.
Making dua in any language outside salah is permissible. Inside salah, dua in a language other than Arabic is makruh tahrimi in the Hanafi school, so keep your own words for after the salam or for any time outside the prayer.
The four schools agree on this.
Explanation
Allah says: "I respond to the invocation of the supplicant when he calls upon Me" (2:186), and "Call upon Me; I will respond to you" (40:60). Neither ayah names a language. The Prophet ﷺ said dua is worship itself, and worship of the heart is open to every believer in the words they have. The four schools agree that dua outside salah may be made in any language.
Arabic duas from the Quran and Sunnah are still the best words, because they were chosen by Allah or taught by His Messenger. A good habit is to begin with one of them, such as Rabbana atina, and then continue in English with your own needs. You can find many in AmalKit's dua collection.
Where you make it matters for salah. After the salam of a fard prayer, at the end of tahajjud, and at any other time outside the prayer, speak in English as long as you like. Inside the prayer, see making dua in your own language in sujood.
Acceptance does not depend on language but on sincerity, lawful income and patience: the Prophet ﷺ said your dua is answered as long as you do not grow impatient and say "I prayed and was not answered". For the full manners, see how to make dua properly.
The evidence
Quran, Surah Al-Baqara 2:186
وَإِذَا سَأَلَكَ عِبَادِى عَنِّى فَإِنِّى قَرِيبٌ ۖ أُجِيبُ دَعْوَةَ ٱلدَّاعِ إِذَا دَعَانِ ۖ فَلْيَسْتَجِيبُوا۟ لِى وَلْيُؤْمِنُوا۟ بِى لَعَلَّهُمْ يَرْشُدُونَ ﴿١٨٦﴾
And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided.
Allah answers whoever calls on Him, with no condition of language.
Quran, Surah Ghafir 40:60
وَقَالَ رَبُّكُمُ ٱدْعُونِىٓ أَسْتَجِبْ لَكُمْ ۚ إِنَّ ٱلَّذِينَ يَسْتَكْبِرُونَ عَنْ عِبَادَتِى سَيَدْخُلُونَ جَهَنَّمَ دَاخِرِينَ ﴿٦٠﴾
And your Lord says, "Call upon Me; I will respond to you." Indeed, those who disdain My worship will enter Hell [rendered] contemptible.
A direct command to make dua, open to every believer.
Sunan Abi Dawud 1479
Graded sahih... الدعاء هو العبادة ...
"Dua is worship."
Dua is worship in itself, which every believer can offer.
Sahih al-Bukhari 6340
Sahih... يستجاب لأحدكم ما لم يعجل ...
"Your dua is answered as long as you are not impatient."
Acceptance is tied to patience and sincerity, not to language.
Where the ruling is recorded
- Radd al-Muhtar (Ibn Abidin), Kitab al-Salah, chapter on the description of prayer, discussion of dua in a language other than Arabic. Non-Arabic dua inside salah is makruh tahrimi; outside salah it is permitted.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.