My translation is a bit different:
タイの人たちに = to Thai people
とってもあまりに長いため = for being so very long
バンコクのことを = Bangkok
いちばんはじめだけとって「クルンテープ」とよびます = calling it only by the very beginning, “Krung Thep”,
Altogether: For being so very long (a name) to the Thai people, Bangkok is called after only the very beginning (of the official name), “Krung Thep”,
The rest is pretty similar.
Can someone explain とって though? The meaning is clear, but I would like to learn how to use it. It appeared previously, but we just brushed over it.