As the denomination's name implies, Jehovah's Witnesses place importance on the name Jehovah. Do they distinguish between Jehovah, Yahweh, the Tetragrammaton, and so on, or do they think these are all acceptable versions of God's name? Also, is there any emphasis placed on how to pronounce 'Jehovah', or is the pronunciation considered non-essential?
Jehovah's Witnesses use whatever form of God's name that is common to Bibles in each language. In modern Hebrew, Jehovah's Witnesses use the "Yahweh" pronunciation. In English, the most common pronunciation is Jehovah. This pronunciation has been used for centuries in English and can be traced back to the Tyndale Bible, the first Bible in English to use Jehovah ("Iehouah") as God's name. "Jehovah" was also popularized by the King James Version, where it uses the name at Psalm 83:18, as well as in a few other scriptures. (But in many modern versions of the KJV, it is now removed there also.)
If someone uses the pronunciation of God's name from another language, we will not think that it's necessarily wrong, but it will sound weird. It's important to be consistent so that we can form a personal connection with that name and the Person that it represents.