I know the New World Translation is not a reliable translation, but why have the other Bible translations changed the original YHWH to LORD?
When a translator encounters a word, he is faced with two choices: he can translate the word or he can transliterate the word. To translate requires finding a word or phrase in the target language that comes closest to the meaning in the original language while still keeping readability in the target language. To transliterate means to give the closest spelling of a word in the target language so that when pronounced in the target language it sounds close to the sound of the word in the original language.
As examples, the word "amen" is a transliteration of the Hebrew word. The word "amen" appears in so many languages as a transliteration, that the translators have just carried on the tradition. The word "baptize" is a transliteration of the Greek word. I suspect in its case, the literal translation would caused ruckus back in the early days of Bible translations. By the 1500's most churches had long substituted sprinkling or pouring for the original meaning of the word "baptism," which means "immerse." Rather than have their translation rejected, the compromise was a transliteration so that the issue would be avoided.
When the King James Version was being translated, it was thought that YHWH was pronounced Jehovah. The spelling is based on German letters, which was common in that period of time in English; hence, 'J' in German has a 'Y' sound and 'V' in German has a 'W' sound. Unfortunately, English has changed since the days of the King James and 'J' and 'V' now have different sounds than they originally had.
The word YHWH appears 6,823 times in the Old Testament text. Most of the time the King James Version translated it as LORD, using capital letters to indicate it has special meaning beyond the English word "lord." About a half-dozen times it was transliterated as Jehovah; mostly to avoid places where the real word for "lord" proceeded YHWH or where the abbreviation for YHWH, Yah proceeded YHWH. Saying the Lord LORD was too awkward, so it became the Lord Jehovah or the LORD Jehovah. The American Standard Version was more consistent. It translated YHWH as Jehovah 5818 times.
In regards to the meaning of YHWH, most scholars refer to a similar word in Hebrew, ehyeh. Ehyeh means "I am" but with the additional idea of continuing action mixed in. It is seen in Exodus 3:13-14, "Then Moses said to God, "Indeed, when I come to the children of Israel and say to them, 'The God of your fathers has sent me to you,' and they say to me, 'What is His name?' what shall I say to them?" And God said to Moses, "I AM WHO I AM." And He said, "Thus you shall say to the children of Israel, 'I AM has sent me to you.'"" The "I AM"'s in this passage are the word ehyeh. Thus many scholars believe that the best translation of YHWH is "He is" or "the Eternal."
YHWH is not God's only name. It is not surprising, no one name could describe such a being as our God. God introduced Himself to Abraham as El-Shaddai ("God Almighty"). It is a mistake to think that YHWH is God's exclusive name or His only real name.
The pronunciation of YHWH is more difficult. Hebrew is written with only the consonant letters. The pronunciation of the words were passed down from generation to generation verbally. We have clues to the pronunciation because YHWH was incorporated into other words. For example, "hallelujah" comes from "hallelu Yah" or "praise Yah," where yahh was an abbreviation for YHWH (the first two letters). You can see it at the end of many Hebrew names: Isaiah (YHWH has saved) or Hezekiah (YHWH has strengthened). It can appear at the beginning of names, such as Jehoshaphat (YHWH has judged) or Joash (YHWH has come to help).
Our real knowledge of the pronunciation of YHWH comes from several very early translations of Hebrew. Shortly after the time of Nehemiah, a group of Jews lived on the island of Elephantine. From their writings we conclude that they pronounced YHWH as "yahu." Clement of Alexander, writing about 200 AD, transliterated YHWH into Greek as iaoue, which would be pronounced "yahweh" in English today.
How did "Yahweh" become "Jehovah?" Radical rabbis, beginning in the fourth century B.C. became concerned that the name YHWH would be misused, violating Exodus 20:7. They decided it was too holy to say, so whenever they came across the name, they would say adhon ("Lord") instead. Eventually, knowledge of how to pronounce YHWH died out.
The Septuagint version translated the Hebrew scriptures into Greek. It was done about 200 B.C. in that translation the word YHWH was translated to the Greek word kurios ("Lord"). In the New Testament, whenever an Old Testament passage was quoted that contained YHWH, the writers used kurios in the Greek. Since these writers were inspired of God, we conclude that God finds "Lord" to be a proper translation of YHWH.
Jumping ahead to about 700 AD, Jewish scholars, known as the Masoretes, realized that knowledge of how to pronounce Hebrew was dying out. They introduced a system of vowel pointers above and below the text, so as to not change the actual sacred writings. These vowel pointers tell the reader what vowel sounds to use for the various words. However, since YHWH was always pronounced adhon when read (and no one probably remembered the real pronunciation by then), the vowels pointers for adhon was placed around YHWH. If the verse contained adhon yhwh, they then put the vowel pointers from the word elohim ("God") around YHWH.
Jumping ahead to about 1200 AD, scholars transliterated the consonants YHWH into European letters of that era (JHVH) and then added the vowels, not knowing they weren't the correct ones. Hence, "Jehovah" was born. It has the consonants of the original YHWH, but the vowels of the Hebrew word for "lord."
Some people today find "Jehovah" repulsive because, unintentional though it may be, it is a made up word. However, since it has come to be associated exclusively with the name of God, one could argue that it is a translation of YHWH, though not a transliteration.
Some, such as the Jehovah's Witnesses, object to using LORD in place of YHWH. However, they are ignoring God's own translation of His name. For example, Jesus quotes Deuteronomy 6:5 in Matthew 22:37, "Jesus said to him, 'You shall love the LORD your God with all your heart, with all your soul, and with all your mind.'" Jesus used the Greek word kurios ("lord") to translate YHWH. This is done consistently in the New Testament, which is inspired by God. Hence, God has shown us that it is proper to translate YHWH as "Lord." The use of all capitals is a convention used by translators to indicate that YHWH is behind the word "Lord" and not the normal Hebrew word adhon.