Was Psalms 45:6 Mistranslated?

Psalms 44/45:6 in the Septuagint reads

ὁ θρόνος σου ὁ θεός εἰς τὸν αἰῶνα τοῦ αἰῶνος ῥάβδος εὐθύτητος ἡ ῥάβδος τῆς βασιλείας σου

The hebrew אֱלֹהִים ('elohiym) was translated into Greek as θεός (Theos)

The Greek text of Hebrews 1:8 reads

Ὁ θρόνος σου ὁ Θεὸς ...

It would seem that the author of Hebrews followed (as other New Testament authors often did) the Septuagint. If there was a mistranslation, someone else made it, and it predates Christianity.

As to why he applied it to the Son, I can only assume he felt it strengthened his argument.

This is an interesting thread to read. I looked at the link @4castle provided, Wescott's comments, as well as several other articles. I searched the Bible in the original languages to find a similar pattern to help explain why it's translated nearly always as, "Your throne, O God, is forever..." rather than how Wescott suggests, "God is your throne forever..."

There is an important aspect we overlook on this passage in Psalms, and it's mentioned in the original post: The NT authors applied this part of Psalm 45 to Jesus, thereby bringing this passage into the category of a Messianic prophecy or Messianic passage.

Because the NT authors, under the guidance of the Holy Spirit, applied this verse directly to Jesus, the verse in Psalms needs to be interpreted with that hindsight as well. Even though the Psalmist may not have realized the Messianic application to the words he wrote, the Holy Spirit knew and ensured the Hebrews author brought it out in the NT text.

It is in this light, therefore, that nearly all scholars translate the passage in Psalms as, "Your throne, O God, is forever..." rather than the way Wescott and the NWT renders it.

I looked at least 10 English translations - including the 1599 Geneva Bible, the Orthodox Jewish, the Expanded, Young's Literal, Complete Jewish, Amplified, Lexham English, RSV, NASV, ASV, Douay-Rheims 1899 American versions - a Spanish, Portuguese, Italian, and French version as well. They all either rendered the passage, "Your throne, O God, is forever..." or a similar syntax. These different versions provide a glimpse of the scholarly opinion of this passage.

Translation teams from 400+ years ago, as well as today, from different countries, and under different supervision have consistently translated this passage, "Your throne, O God, is forever..." Knowing that scholars take into consideration not only the words, grammar, and historical syntax, as well as letting the Bible interpret itself (like viewing an OT passage in light of the Messianic application or fulfillment), it is clear to see what Biblical scholars believe to be the most accurate translation of the passage in Psalms: "Your throne, O God, is forever..."

According to Bible scholar B. F. Westcott, this is likely a Greek to English mistranslation, not a Hebrew to Greek mistranslation. Based on the context of the verse, he believes a better rendering would be: "God is Thy throne" or "Thy throne is God".

He says (bold mine, italics original):

The LXX. admits of two renderings: [ho the·osʹ] can be taken as a vocative in both cases (Thy throne, O God, . . . therefore, O God, Thy God . . . ) or it can be taken as the subject (or the predicate) in the first case (God is Thy throne, or Thy throne is God . . . ), and in apposition to [ho the·osʹ sou] in the second case (Therefore God, even Thy God . . . ). . . . It is scarcely possible that [’Elo·himʹ] in the original can be addressed to the king. The presumption therefore is against the belief that [ho the·osʹ] is a vocative in the LXX. Thus on the whole it seems best to adopt in the first clause the rendering: God is Thy throne (or, Thy throne is God), that is ‘Thy kingdom is founded upon God, the immovable Rock.’

—The Epistle to the Hebrews (London, 1889), pp. 25, 26.

There is at least one Bible translation which uses this rendering: the New World Translation.

God is your throne forever and ever;
The scepter of your kingdom is a scepter of uprightness.
You loved righteousness, and you hated wickedness.
That is why God, your God, has anointed you with the oil of exultation more than your companions.
—Psalm 45:6, 7

But about the Son, he says: “God is your throne forever and ever, and the scepter of your Kingdom is the scepter of uprightness. You loved righteousness, and you hated lawlessness. That is why God, your God, anointed you with the oil of exultation more than your companions.”
—Hebrews 1:8, 9

Jehovah's Witnesses have also published an article discussing this translation of Hebrews 1:8.

RS reads: “Of the Son he says, ‘Thy throne, O God, is for ever and ever.’” (KJ, NE, TEV, Dy, JB, NAB have similar renderings.) However, NW reads: “But with reference to the Son: ‘God is your throne forever and ever.’” (AT, Mo, TC, By convey the same idea.)

Which rendering is harmonious with the context? The preceding verses say that God is speaking, not that he is being addressed; and the following verse uses the expression “God, thy God,” showing that the one addressed is not the Most High God but is a worshiper of that God. Hebrews 1:8 quotes from Psalm 45:6, which originally was addressed to a human king of Israel. Obviously, the Bible writer of this psalm did not think that this human king was Almighty God. Rather, Psalm 45:6, in RS, reads “Your divine throne.” (NE says, “Your throne is like God’s throne.” JP [verse 7]: “Thy throne given of God.”) Solomon, who was possibly the king originally addressed in Psalm 45, was said to sit “upon Jehovah’s throne.” (1 Chron. 29:23, NW) In harmony with the fact that God is the “throne,” or Source and Upholder of Christ’s kingship, Daniel 7:13, 14 and Luke 1:32 show that God confers such authority on him.