بسم الله الرحمن الرحيم
(Fatwa: 368/319/SN=04/1437)
(1) Whether it is fardh salah or nafl salah it is unlawful and makrooh tahrimi to read dua in Urdu, English or any language other than Arabic. However you may supplicate Allah in any language after completing your salah.
(ودعا بالعربية وحرم بغيرها (درمختار) وقال الشامى: ولا يبعد أن يكون الدعاء بالفارسية فى الصلاة مكروها تحريماً فى الصلاة (درمختار مع الشامى 2/233، 234، ط: زكريا).
(2) It is better if you join any madrasa and study Arabic as well as other sciences. If not, then read Arabic language by any reliable and competent Alim on daily basis as per his guidance. Also try to learn Arabic through studying Arabic books and listening to Arabic lectures.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband