But by my name JEHOVAH was I not known to them (Isaiah 12)

So, Isaiah chapter twelve, huh? There's not much in this short chapter, so I'm going to talk about the name "Jehovah". There's a word in the Hebrew that is considered to be the name of God, but that name is considered so holy by observant Jews that they never actually say the name. Instead, they usually say "Lord" (Hebrew "Adonay") or, when being informal, simply "the Name" (Hebrew "Hashem"). Accordingly, most Bibles translate this name as "Lord", or sometimes "LORD" to clarify that it's this specific name. The KJV translates it "LORD" 6,510 times, but "JEHOVAH" four times, including here.

Okay, this is vague memories from Hebrew school 40 years ago, so it may not be 100% accurate; I wish I had an observant Jew who was a reader who could chime in. Hebrew in the Torah in particular is written entirely in consonants, the vowels being left out. The Hebrew alphabet is actually entirely consonants, with vowels being indicated (when used) by small marks generally above or below the letters. The name of God, as written in the Torah, is the four letters "יהוה", equivalent more or less to the Latin "YHVH". Usually vowels aren't used, because the name is not meant to be pronounced. However, in some Hebrew texts, it's written as "יְהֹוָה"; those vowels aren't meant to be taken as part of the name, but rather--if I'm recalling correctly--it's the vowels for "Adonay" to remind you that you're supposed to say "Adonay". So here's the thing: if you do decide to pronounce "יְהֹוָה" as if it's an actual name, it's "Y'HOVAH", which has been sometimes rendered in Latin as "IEHOVAH", which eventually led to the English "JEHOVAH". So "Jehovah" is not the name of God; it's an Anglicized version of a Latinized version of a mispronounced Hebrew word! So that's my Hebrew soapbox for this chapter, anyway. I hope it was more enlightening than confusing.