Psalm 45 is a wedding song for the marriage of a king of Israel. At verse 7a the lyric says:
כִּסְאֲךָ אֱלֹהִים, עוֹלָם וָעֶד
The Jewish Greek translation which came to be called the Septuagint renders this verse this way: 'Your throne, God, is forever and ever.' So also Aquila and Theodotion.
According to this translation, the king who is addressed in the preceding verses is addressed as 'God' here. Abraham Cohen in The Soncino Books of the Bible states that 'this appears to be the obvious translation but does not suit the context.'
Sa'adya Gaon, Ibn Ezra, and Rashi depart from this reading, but each of them translate this passage differently. 'God establishes your throne' (Gaon). 'Your throne is the throne of God' (Ibn Ezra). Rashi, who reads this psalm allegorically, understands 'elohim as a vocative like the Septuagint, but he takes it as an address to the Torah scholar, and he renders 'elohim as 'judge' (as Onkelos and he do at Exodus 7:1 and elsewhere): 'Your throne, O judge.' Yet in the next verse 'elohim (2x) means 'God.'
Prior to Rashi, the Targum also understands 'elohim as a vocative, but to insure that it might not be understood as an address to the king of Israel in the sense of 'God', it replaces 'elohim with the Shem Hameforash abbreviated: 'The throne of your glory, O Yy, lasts forever and ever.' But the Hebrew interpreted as an address to God in the midst of a poem addressed to the king and to his bride seems to be a misconstrual, for nowhere else are words directed to God.
Are there any translators or commentators who translate 'elohim in Psalm 45:7a as a vocative in the sense of 'God' as do the Septuagint, Aquila, and Theodotion?