@Michael *******
in order to buy a train ticket online you do need your passport number to buy it, the same as a Thai needing their ID number. Someone else can buy it for you, but they do need your passport number to do it. I buy quite a few train tickets online using
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Use the drop-down menu to change languages. You should be able to use this site to buy your train tickets from anywhere in the world. It is the official train ticket portal. You get an email with the ticket, then just print it out.