Prayer in the language one understands

Hi,

One who does not understand the Hebrew amidah should use a proper translation, rather than simply create his own prayer.

[Note: This is separate from one's ability to add afterward; it is simply the minimum.]

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:70:4)

Have a great day,
Mordechai