I personally believe that Yochanan either wrote it in Hebrew, or Aramaic, then it was translated to Greek, at some point.
Scribes wrote 'in time', and they did this up until very recently. I personally believe that the Apostle writings were in Hebrew & Aramaic, notations, then compiled and transferred, into the Greek. Some of the writings were also in Greek, most likely, and even another language.
Hence, we have what we have, textually, and in English, the KJV, although a few words and names don't literally match, they did a good job of keeping words in, in some manner.
So, for example, when Jesus calls Peter Satan, supposedly, in the Greek, there is a pause, 'and then Jesus said', after Jesus says, "Get behind me Satan!".
The KJV, maintains this pause, with a :, whereas some Bibles do not maintain a pause.
For many verses, the KJV is a good standby.