Prayer is speaking to God, and, as with any conversation, it is possible for others to overhear what we say. We assume that Satan can and does “eavesdrop” on our prayers—that is, he can hear what we pray about. This should not be of major concern to the child of God.
The Bible records many prayers from saints who prayed out loud, in their own language, with no fear that Satan might be eavesdropping:
The above cases have at least two things in common:
1) Satan is not mentioned even once.
2) Those who prayed simply talked to God in a heartfelt, straightforward manner.
3) The prayer was answered.
As they prayed, Daniel and David and Hezekiah and Hannah focused on God and God alone. If the thought that Satan was listening ever crossed the minds—and it doesn’t seem that it did—their attitude would likely have been, “So what?” Satan might be eavesdropping—so what? The devil will do his worst—so what? We’re not talking to him; we’re talking to the Sovereign God of the universe! Our God will hear our cry and act on our behalf, regardless of what Satan hears or doesn’t hear, or what he does or doesn’t do.
Satan can eavesdrop if he wants, but he is not stronger than the Holy Spirit, who “prays for us with groanings that cannot be expressed in words. And the Father who knows all hearts knows what the Spirit is saying, for the Spirit pleads for us believers in harmony with God’s own will” (Romans 8:26–27, NLT).
Satan and his demonic hordes have absolutely no power to prevent God from answering our prayers according to His will. So, there is no need to stop verbalizing our prayers to keep Satan from hearing them. And there is no need to employ a “heavenly language” to try to “fool” Satan. God hears, and that’s all that matters. Whether Satan and his demons hear and understand our prayers is irrelevant.