Mantras and prayers are commands or requests for aid: what matters is that the intended recipient hears and understands the meaning, so it can be acted upon.
Many words or sounds in our modern languages have opposite or contradictory meanings. So if I say a word in English, that same sound has the opposite meaning in other languages: which one should apply? The meaning in my mind, or the meaning in the mind of the listener? Nature does not recognize either of them: the actual vibration of the sound creates an effect, no matter what "meanings" we have in our minds. Mantras are those root sounds: they create precise effects, and are mostly unrelated to modern languages.
For instance, if you learn a mantra from the black lodge, you may believe it is good and true, but it is not: it is black. So, your beliefs and ideas about it, your interpretation, does not matter. The pronounced mantra creates the effect that the black lodge wants.
Similarly, when you chant a mantra or prayer that is pure and good, you may not understand it or even have a clue about its meaning, but it will have its effect anyway. However, if you do know the meaning, and you invest your consciousness into each vowel, then power is magnified and extended.