It's Minnanese, a chinese dialect commonly spoken in Taiwan. The song is a popular Karaoke song if you are 50+ Taiwanese.

i'm 95% sure the video is from taiwan and they're singing in
Taiwanese Minnan (臺灣閩南語), commonly known as Taiwanese (臺灣話; 臺語), is a variant of the Hokkien form of the Min Nan Chinese language spoken by about 70% of the population of Taiwan.
http://en.wikipedia.org/wiki/Taiwanese_Minnan love his choice of tie-wear!

subtitles are chinese and i think they are singing in vietnamese.

Definitely NOT Japanese. Try Chinese.

Not Japanese.

I am pretty sure that isn't Japanese.