Please could you tell me if what I am doing is permissible or not? Arabic is not my mother tongue, and sometimes when I pray, after I say something, I repeat it in English in my mind so as to increase my focus (khushoo‘) and to focus more in my prayer. Hence for example after I say “Sami‘a Allahu liman hamidah” in Arabic, I repeat it in my mind in English (“Allah hears those who praise Him”). Is this permissible or not?.
There is nothing wrong with what you are doing to focus on the meanings of the words and adhkaar of the prayer in English after saying them in Arabic. This comes under the heading of pondering the meaning and keeping it in mind. That is so long as you do not utter it; rather you say it to yourself in your mind, because the one who is praying is not allowed to say these words in anything but Arabic if he is able to say them in Arabic. This has been discussed previously in the answer to question no. 3471.
And Allaah knows best.