I don’t think the halacha of davening in an alternate language would depend on what the angels can understand. We aren’t davening to them after all. Also, as far as I know it is only Aramaic that angels can’t understand, not all languages besides L”K.
If the choice is between davnening in L”K and not understand vs. davening in English and understanding- it seems that people generally do the former. For instance, the kavanah that we have for Shemoneh Esrei is not even a scratch of what the Anshei Kneses Hagedolah had in mind, yet even though we don’t understand the depths of what we are saying, we still don’t switch to English.