Shaykh al-Islam Ibn Taymiyah was asked about a man who made du’aa’ in ungrammatical language, and a man said to him that Allaah would not accept a du’aa’ spoken in ungrammatical language.
Whoever voiced this opinion is a sinner who has gone against the Qur’aan and Sunnah and the view of the salaf. For whoever calls upon Allaah, devoting his worship sincerely and purely to Him, calling upon him with a du’aa’ that is permissible, Allaah will listen to him and respond to his du’aa’, whether it is in proper Arabic or in ungrammatical language. The opinion mentioned has no basis, rather the one who makes du’aa’, if he is not used to speaking in grammatical Arabic, he should not force himself to do so. One of the salaf said, if a person forces himself to speak grammatical Arabic, he will not be focused in his heart. Similarly it is makrooh to force oneself to make the words of the du’aa’ rhyme; if that happens spontaneously, then it is fine, for the du’aa’ should come from the heart, and the tongue should simply follow the heart. Whoever focuses in his du’aa’ on making the words grammatically correct will have less focus in his heart. Therefore the one who is in urgent need should pray from the heart with whatever words Allaah inspires him to say, without preparing it beforehand. This is something which every believer finds in his heart. It is permissible to make du’aa’ in Arabic or in languages other than Arabic. Allaah knows the desire of the one who is making du’aa’, even if he cannot speak Arabic correctly, for He understands all languages and understands the needs of those who speak different languages.