which superlative is true : the most lovely or the loveliest?
As an American English-speaker, I would consider "most lovely" to be incorrect. I was taught that if you can use -er or -est it is incorrect or at least in bad form to use "more" or "most" instead. For example: "beautifuler" is not a real word, so you would say "more beautiful". "Loveliest" is a word, so you would not say "most lovely" (the exception being in older and more formal texts). You might be able to get away with it, but it is bad form in my opinion/experience for modern usage. Of course, this is simply my personal experience, and I could quite possibly be way off base.