I'm not a Buddhist, but I like learning about languages, and this video shows something which I think is very interesting from a linguistics point of view:
(No, it's not what's on his chest, but having said that, I'll just point out that in China and Chinese-speaking communities, the swastika is a good-luck charm and a character that means '10,000', 'eternity', 'myriad', 'blessings' and 'goodness'. It is pronounced as 'wan4' in Mandarin.)
The soundtrack is a Buddhist chant called 大悲咒 ('The Mantra of Avalokiteshvara' / 'The Mantra of Great Compassion') and what's really interesting is that many thousands of years ago, Buddhist monks used Chinese characters to record the sounds of Sanskrit. This is akin to using the Latin alphabet to render 大悲咒 as 'Da Bei Zhou' instead of 'The Mantra of Great Compassion'.
The first two lines are written as
which not only look nonsensical, but are normally read in Mandarin as
nan2 wu2 he1 luo2 dan4 na4 duo1 luo2 ye4 ye1 etc.
But in the chant, they're read as
ná mó ·hé là dá nā ·duō là ya yē ná mó ·ā lì yē pó lú qié dì...
while the original Sanskrit is rendered with the Latin alphabet as:
Namo Ratna Trayaya, Namo Arya Jnana...
So the language of the chant in the video is neither Mandarin nor Sanskrit, but a hybrid. In addition to the sounds of Sanskrit, the meaning of each Sanskrit word was also noted, so monks nowadays do know the meaning of what they're chanting.
I think it's possible to use the surviving Chinese texts and chants to reconstruct Sanskrit texts and pronunciation, and to infer that modern Mandarin wasn't the language the Chinese characters were originally read in. I don't know if this is the case, and which Chinese language could have been used, so if anyone knows this, do let me know!