Praise be to Allah.
With regard to following the imam’s recitation in a book in which there is a translation of the meanings of the Qur’aan, this requires further discussion:
If he says something from the book whilst following the imam’s recitation [i.e., moving his lips whilst reading], then his prayer is invalid, because the translation of the meaning of the Qur’aan is regarded as a commentary on it (tafseer), and it is not Qur’aan according to the consensus of the scholars and it does not come under the same rulings as Qur’aan, so these words invalidate the prayer.
See: Fataawa al-Lajnah al-Daa’imah li’l-Buhooth al-‘Ilmiyyah wa’l-Ifta’, 4/165
If it is limited to following the words by looking and thinking without speaking, then the prayer is valid even though it is makrooh.
al-Nawawi said: “If he turns the pages sometimes during his prayer, it is not invalidated, and if he looks at a book other than the Qur’aan and reads that in his mind, it does not invalidate his prayer, even if it is done for a long time, but it is makrooh.
End quote from al-Majmoo‘, 4/95
Al-Mardaawi said: Prayer does not become invalidated by looking for a long time in a book if he reads it in his mind, if he does not actually utter the words, according to the correct view. ... It was narrated from Imam Ahmad that he did that. And it was said that it does invalidate the prayer.
End quote from al-Insaaf, 2/98
Something similar to this was said in Fath al-Qadeer, 1/403
Following the recitation by looking in the book and pondering the meaning is permissible, although it is makrooh, but this description of it being makrooh does not apply if there is a need for that, because the basic principle according to the fuqaha’ is that that which is makrooh becomes permissible if there is a need.
Seeking to focus properly in prayer and understand the meaning of what the imam is reciting is a kind of need that makes this no longer makrooh, because understanding the meaning of the verses is something that is important for the person praying behind the imam, so that he may ponder them and think of their meanings.
Something similar to this was stated in a fatwa by Shaykh Ibn Baaz, that it is permissible for the person praying qiyaam al-layl behind the imam to hold a Mushaf in which there is tafseer, and if he does not understand a word he may look at its meaning. This was mentioned in the answer to question number 9505.
But what is better than that is to strive to learn Arabic and learn the Holy Qur’aan and its meanings, so that it will be easy for you to ponder it and focus properly in prayer, and you will not need to carry this book and look at it whilst praying.
And Allah knows best.