Personally, I wouldn't try to sing in a language I don't speak, apart from the odd phrase or refrain or something. I don't see how you can give the words any expression, or even stress them properly, if you can't understand them.

If people are posting words in a foreign language, it's worse than useless to try to post a phonetic pronunciation. Because English is not phonetically written in the first place, there is no univerally understood way of writing out sounds in a way that will approximate to the correct pronunciation. In addition, many languages have sounds that don't occur in English. If you've ever tried to use a foreign-language phrase book you'll know the problems.

The only sensible way is to post the original words and leave it to the reader to find out how they should sound, possibly by linking with Youtube videos or using a translation program that includes pronunciation.

Marje