Do previous prayers and Quran recitations performed in English become invalid, and what are the correct practices for a non-Arabic-speaking believer in prayer and recitation?

Surat Al-Fatihah must be memorized for prayer, and reciting the Qur'an in a language other than Arabic is not valid unless one is unable to do so, as some jurists hold. As for the takbirat (utterances of "Allahu Akbar") of the prayer, the tasbih (utterances of "Subhanallah"), and the tashahhud (testimony of faith), one must learn them and perform them in Arabic. If the worshiper is unable, then they may say them in their own language. And whoever has been praying with translation must stop and learn Arabic to perform the prayer correctly.