All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Not learning the minimum of the Arabic language, by which the prayer is valid, that's to say the opening chapter of the Quran (Al-Faatihah) and another chapter, and some other supplications, affects faith; and faith cannot be achieved except by the prayer. However, the prayer is not valid except by reading the opening chapter of the Quran (Al-Faatihah). The Prophet said: "Whoever prays without reciting chapter Al-Faatihah, his prayer is invalid." [Al-Bukhari and Muslim] However, not learning (or memorizing) more than what has been mentioned, does not affect faith. But it is better for a Muslim to learn the language of the Quran as much as he can. It is not valid to read the Quran except in the Arabic language. Nevertheless, if you cannot read the Quran in Arabic, you can read the interpretation of its meaning in other languages. The Prophet urged people to read the Quran as he said: "One who reads in the Quran perfectly is associated with the noble, upright, recording angels; and he who falters in it, and finds it difficult to recite, will have a double reward." [Muslim]
Allaah knows best.