In many circumstances, "ae" is how the Greek dipthong "ai" (alpha-iota) - pronounced "eh" - is transliterated into Latin, etc
Examples:
Aisopos (Grk.) =>
Aesop (L, Engl.)
Aither (Grk.) => Aether (L) => Ether (Engl.)
Aisthetikos (Grk.) => Aestheticus (L) => Aesthetic (Engl.)