In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is not forbidden to say the English meanings of the prayer formulas in your mind without articulating the sounds.
In responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
It is not forbidden to say the English meanings of the prayer formulas in your mind without articulating the sounds. There is nothing wrong if one is offering supplications in one’s language after reading the prescribed formulas or words.
Many scholars view that in prayer, especially obligatory prayers, one should use only the Arabic and avoid any other language. However, others allow it to offer supplications and reading phrases such as those you mentioned.
Having said this, I would like to state: Once you have mastered Arabic enough to read the prescribed portions of the Quran or the Prophetic duaas in Arabic, you may offer extra supplications in your language.
Almighty Allah knows best.