Evidently, this is based on the man-made assumption that if it is not pronounced as it was originally pronounced in ancient Hebrew, then it is "not God's name."
The idea that the Holy Name has be pronounced and spelled as it was originally pronounced or spelled in order for it to be God's name is actually what is man-made. God never presented such an idea. You will not find such a thought ever presented in the Bible. Such a doctrine is itself man-made.
If that idea is true, then every English form of any name from the Bible is a "manmade guess" and are not really the names of the persons involved, including any form of the name of God's son, since no one on earth today knows for a certainty what the original Hebrew sounded like. The sounds often used are themselves based on theory, in effect, assumptions.
In Bible times, names did change in spelling from one language to another as can be seen from Koine Greek of the New Testament, as well as many other writings in various languages from that time.
As far as the Holy Name being presented in English as "Jehovah", this is a direct transliteration from the Hebrew Masoretic text. I cannot say that this means that this is the way it was originally pronounced; it doesn't really matter. There is no command in the Bible that God's name or any other name has to be pronounced exactly as it was in ancient Hebrew or else it is a false name. This idea is invented by man, is actually a false doctrine.
Nevertheless, some have produced a hypothesis, which has often been presented as fact, that the Masoretes took vowels from other words (from their words often transliterated as Adonai and/or Elohim) to form their word that transliterates as Jehovah / Yehowah / Iehouah, etc. Thus they claim that "Jehovah" is a hybrid name. However, no evidence that the Masoretes did such a thing can be found; there is no reason to think that the Masoretes did not endeavor to present vowels for the Holy Name as they thought it to have been originally pronounced. No, we do not know that "Jehovah" in English is the exact same way it was pronounced in ancient Hebrew; it is certain that "Jesus" is not the way the name of His son was pronounced in ancient Hebrew. We do not know that Elijah was the way this name was pronounced in ancient Hebrew, nor do we know for a certainty how it was originally pronounced. Indeed, in the New Testament, a transliteration of that name is Elias; the New Testament does not present Elias as being a different name, but as the same name, despite the way many today may speak of the two forms as though they are two different names.
The truth is we do not know for a certainty how any of the names in the Bible were originally pronounced. Any claim otherwise is false, since once one examines the basis of such claims, one finds many assumptions being presented, often as though fact.
It is claimed that the literature of the JWs claims that Raymundus Martini coined the form "Jehova", and God's true religion would not need to guess how the name came to be, His true religion would know it from Jesus.
I am not with the JWs, and we make no claims about any "true religion" except that given by Jesus and the apostles. It is simply a fact that Raymudus Martini never presented the Holy Name as "Jehovah". It is simply a fact that "Jehovah" is a direct transliteration from the Masoretic text which was in existence long before Martini.
Nevertheless, I do not believe that the JW writers claim to be infallible. Regardless, we should not accept what they say as being fact. There are many out there, including many so-called experts, scholars, etc., who present many of their assumptions as being fact, but one should always look for the basis, to see if what is being said is indeed fact, or based on some kind of assumption(s). In all claims being made to have found the original pronunciation, despite the claims made, if examined closely, one will see that there are assumptions (usually accepted and presented as being facts) of sounds attributed to the ancient Hebrew.
It is claimed that Jesus did not ever rebuke the Jews for not using it or use any translation of YHWH as Almighty God's name, at least not as recorded in the original Greek NT.
We do not have the originals of the New Testament writings, but we can see that the name has been changed in the extant Greek NT manuscripts. It is apparent that someone has changed the Holy Name to forms of the words often transliterated as KURIOS and THEOS, and possibly some other words, such as DUNAMIS. If Jesus declared his coming in the name of KURIOS rather than the name prophesied that he was to come in in Deuteronomy 18:15-19, then, according to that prophecy (Deuteronomy 18:20-22), he was actually a false prophet, speaking in the name of another rather than in the name of Jehovah. -- Deuteronomy 18:20.
It is true that we do not know for a certain why God's Holy Name was changed to other forms in the copies, but there is evidence that suggests that towards the end of the first century and the beginning of the second century, the Jews were confiscating and destroying all Christian writings that contained the Holy Name. Thus, we can see how Christian copyists might have changed the Holy Name to other words in order to keep the Jews from destroying all copies of what became the NT. Additionally, evidence suggests that they did the same with the LXX.
