In simple terms.... The tetragrammatom in ancient HEBREW, it is actually a sentence 'he causes what he wills' and what a suprise, or not really... That HEBREW sentence that the JW's claim is gods name... is not anywhere in the GREEK writings.
Bare in mind it isnt just a different language but a different slphabet. The JW's WRONGLY replace LORD in the NT not only with the tetragrammaton sentence, but with the name jehovah.
700 years after jesus died, copyists assumed there may be a code in the old testament and used two terms used for god in the old testament, YHWH and LORD or in hebrew Adonai. They took the consonants from adonai and added them to YHWH to make YaHoWaH, or in latin JaHoVaH.
So not only have they assumed a hebrew sentence is somehow supposed to be in a GREEK text, they then say it is supposed to be this mish mash of YHWH and ADONAI. It is shameful... They know they shouldnt be doing it, hence they add an excuse to the bible itself in its glossary.