Conversation:

Well, I just want to note that there are (and were since the ancient Greece) 2 letters for th. Theta, which looks somewhat like an O with a horizontal line in the middle, represents the voiceless th, like in "through". Delta, which in its capital form looks like a triangle, represents the th as it appears in "though". In contrast, the Greek alphabet never had specific letters for sounds like d or h, the first often written as "nt", the latter appearing as a '.

Just as a note.