The world is full of beautiful languages and I think we should all try to get acquainted with as many of them as possible. If you are thinking about singing a song in an unfamiliar language, here are some resources that might help you.
Keep in mind that most languages have regional variations, and the conventions of singing often differ from those of speaking. For example, if you consulted native English speakers from New York, New Orleans, Dublin, and Singapore, they might give you four different pronunciations for a particular word. When we sing in English, we usually try to find a kind of average, where we can be understood by people from all those places without sounding quite like any of them. We also might pronounce a word one way if the text is very formal, and another way if it is more casual.
The same can apply to other languages. The purpose is to effectively communicate the text, and these are my opinions on how to do so with my own compositions. I use the International Phonetic Alphabet for reference, so it will help to be very familiar with that before proceeding.