Is it forbidden to pronounce or say the Name of God (YHVH) as it was written and spoken in the Hebrew language thousands of years ago ? I have always thought that it was.... so I did some research and found the following:
In Exodus 3: 13-15 God tells Moses that His name is "YHVH" and that this is how he should be MENTIONED in every generation ....
And Moses said to God, "Behold I come to the children of Israel, and I 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?"
יגוַיֹּ֨אמֶר משֶׁ֜ה אֶל־הָֽאֱלֹהִ֗ים הִנֵּ֨ה אָֽנֹכִ֣י בָא֘ אֶל־בְּנֵ֣י יִשְׂרָאֵל֒ וְאָֽמַרְתִּ֣י לָהֶ֔ם אֱלֹהֵ֥י אֲבֽוֹתֵיכֶ֖ם שְׁלָחַ֣נִי אֲלֵיכֶ֑ם וְאָֽמְרוּ־לִ֣י מַה־שְּׁמ֔וֹ מָ֥ה אֹמַ֖ר אֲלֵהֶֽם:
God said to Moses, "Ehyeh asher ehyeh (I will be what I will be)," and He said, "So shall you say to the children of Israel, 'Ehyeh (I will be) has sent me to you.'"
ידוַיֹּ֤אמֶר אֱלֹהִים֙ אֶל־משֶׁ֔ה אֶֽהְיֶ֖ה אֲשֶׁ֣ר אֶֽהְיֶ֑ה וַיֹּ֗אמֶר כֹּ֤ה תֹאמַר֙ לִבְנֵ֣י יִשְׂרָאֵ֔ל אֶֽהְיֶ֖ה שְׁלָחַ֥נִי אֲלֵיכֶֽם:
And God said further to Moses, "So shall you say to the children of Israel, 'The Lord God of your forefathers, the God of Abraham, the God of Isaac, and the God of Jacob, has sent me to you.' This is My NAME forever, and this is how I should be MENTIONED in every generation.
טווַיֹּ֩אמֶר֩ ע֨וֹד אֱלֹהִ֜ים אֶל־משֶׁ֗ה כֹּ֣ה תֹאמַר֘ אֶל־בְּנֵ֣י יִשְׂרָאֵל֒ יְהֹוָ֞ה אֱלֹהֵ֣י אֲבֹֽתֵיכֶ֗ם אֱלֹהֵ֨י אַבְרָהָ֜ם אֱלֹהֵ֥י יִצְחָ֛ק וֵֽאלֹהֵ֥י יַֽעֲקֹ֖ב שְׁלָחַ֣נִי אֲלֵיכֶ֑ם זֶה־שְּׁמִ֣י לְעֹלָ֔ם וְזֶ֥ה זִכְרִ֖י לְדֹ֥ר דֹּֽר:
And in Exodus 9:16 God says :
But, for this [reason] I have allowed you to stand, in order to show you My strength and in order to DECLARE my Name all over the earth.
טזוְאוּלָ֗ם בַּֽעֲב֥וּר זֹאת֙ הֶֽעֱמַדְתִּ֔יךָ בַּֽעֲב֖וּר הַרְאֹֽתְךָ֣ אֶת־כֹּחִ֑י וּלְמַ֛עַן סַפֵּ֥ר שְׁמִ֖י בְּכָל־הָאָֽרֶץ:
Pronouncing the Name of God :
Nothing in the Torah prohibits a person from pronouncing the Name of God. Indeed, it is evident from scripture that God's Name was pronounced routinely. Many common Hebrew names contain "Yah" or "Yahu," part of God's four-letter Name. The Name was pronounced as part of daily services in the Temple.
The Mishnah confirms that there was no prohibition against pronouncing The Name in ancient times. In fact, the Mishnah recommends using God's Name as a routine greeting to a fellow Jew. Berakhot 9:5. However, by the time of the Talmud, it was the custom to use substitute Names for God. Some rabbis asserted that a person who pronounces YHVH according to its letters (instead of using a substitute) has no place in the World to Come, and should be put to death. Instead of pronouncing the four-letter Name, we usually substitute the Name "Adonai," or simply say "Ha-Shem" (lit. The Name).
Although the prohibition on pronunciation applies only to the four-letter Name, Jews customarily do not pronounce any of God's many Names except in prayer or study. The usual practice is to substitute letters or syllables, so that Adonai becomes Adoshem or Ha-Shem; Elohaynu and Elohim become Elokaynu and Elokim; Eil becomes Keil, etc.
With the Temple destroyed and the prohibition on pronouncing The Name outside of the Temple, pronunciation of the Name fell into disuse. Scholars passed down knowledge of the correct pronunciation of YHVH for many generations, but eventually the correct pronunciation was lost, and we no longer know it with any certainty. We do not know what vowels were used, or even whether the Vav in the Name was a vowel or a consonant. See Hebrew Alphabet for more information about the difficulties in pronouncing Hebrew. Some religious scholars suggest that the Name was pronounced "Yahweh," but others do not find this pronunciation particularly persuasive. Historian Flavius Josephus, who was born a kohein at a time when the pronunciation of the Name was still known, said that the name was four vowels (War of the Jews, Book V, Chapter 5), probably referring to the fact that each of the four consonants in the name can serve in Hebrew as a vowel or vowel marker. See Hebrew Alphabet.
Some people render the four-letter Name as "Jehovah," but this pronunciation is particularly unlikely. The word "Jehovah" comes from the fact that ancient Jewish texts used to put the vowels of the Name "Adonai" (the usual substitute for YHVH) under the consonants of YHVH to remind people not to pronounce YHVH as written. A sixteenth century German Christian scribe, while transliterating the Bible into Latin for the Pope, wrote the Name out as it appeared in his texts, with the consonants of YHVH and the vowels of Adonai, and came up with the word JeHoVaH ("J" is pronounced "Y" in German), and the name stuck. via: http://www.jewfaq.org/name.htm