Why do Jehovah’s Witnesses call their god "Jehovah"...?

Mark Lawrence 

Why do Jehovah’s Witnesses call their god "Jehovah", when that name has almost nothing in common with the actual name of the god used in the Torah?

With respect to the question poser, this question demonstrates a very deep ignorance of both language and history apropos, not to mention the specious use of “their god”, which suggests that it’s a different god, as opposed to the God.

The name of God in not only the Torah, but indeed the OT throughout, is יהוה, Yod, Heh, Wah, Heh, read right to left, and is written in consonants since ancient Hebrew did not include vowels. Therefore the pronunciation Yahweh is, at best, a guess.

The Masoretic texts include the vowel points, so instead of יהוה we have יְהוָ֣ה in the Leningrad Codex, for example. Below is the Aleppo codex; you can see the divine name with the vowel points.

Literally hundreds of such manuscripts have been found, telling us that the original pronunciation was, in fact, very close to the English rendering Jehovah.

The original Hebrew name of God re-discovered in 1,000 Bible manuscripts

On January 21, 2018, Bible Scholar Nehemia Gordon and his team of researchers discovered the 1,000th Hebrew Bible manuscript containing the original name of God in Hebrew with vowels.

https://religionnews.com/2018/01/25/the-original-hebrew-name-of-god-re-discovered-in-1000-bible-manuscripts/