What is the ruling of the Shari'ah concerning one who leads non-Arabs in prayer and recites in a colloquial (broken) dialect, on the pretext of winning their hearts and endearing Islam to them?

Reciting the Qur’an in colloquial Arabic is not permissible. Whoever intentionally does so, while being able to recite correctly, has committed a grave transgression that could lead to disbelief (kufr) and expulsion from the faith if the distortion results in altering letters or changing meanings. The duty is to convey the Qur’an as it was revealed, for Imam Ibn al-Jazari said: “Applying Tajweed is an obligatory duty; whoever does not apply Tajweed to the Qur’an is a sinner, because Allah revealed it with Tajweed, and in this manner it reached us.” And Allah the Almighty has commanded its measured recitation (tartil).