Even if I tell him how things really are, we don't speak the same language.
This is because he's taken the propaganda as truth.
ご質問ありがとうございます。
"Even if I tell him how things really are,"=「彼に物事が実際にどうなっているか伝えても」
"we don't speak the same language."=「話が嚙み合わない。」
"This is because he's taken the propaganda as truth."=「それは彼がプロパガンダを真実だと思い込んでいるからだ。」
ご参考に。