It's Bulgarian! And one of my favorite psalms! Thank you, Google Translator!
"Remember, Lord, King David /
and all his meekness, Hallelujah /
how he swore to the LORD /
'I will not give sleep to mine eyes /
till I find a place for the Lord.' Hallelujah."
The subtitles may be, but the singing is definitely Slavonic.
You could say with much more justification: "The subtitles may be and the singing is naturally Slavonic." From the Wiki:
"Old Church Slavonic, also known as Old Bulgarian,[1][2][3] or Old Macedonian,[4][5][6] was the first literary Slavic language, based on the old Slavic dialect of the Thessalonica region, employed by the 9th century Byzantine Greek[7] missionaries, Saints Cyril and Methodius, who used it for translation of the Bible and other Ancient Greek ecclesiastical texts, and for some of their own writings. It played a great role in the history of Slavic languages and served as a basis and model for later Church Slavonic traditions, where Church Slavonic is used as a liturgical language to this day by some Orthodox and Greek-Catholic Churches of the Slavic peoples."
FYI: Services in most South and East Slavic Churches contain both the modern vernacular and Church Slavonic. Again from the Wiki: "Historically, this language is derived from Old Church Slavonic by adapting pronunciation and orthography and replacing some old and obscure words and expressions with their vernacular counterparts."
BTW, I am not familiar with the term "Slavonic singing." Do you instead mean "Slavic" singing? For example, the Bulgarian Church uses both Byzantine chanting/tones and tones and choral compositions from Slavic nations and and composers.
