I know no Arabic, but I have heard different dialects from my friends who do speak Arabic. Often when people ask for *the* Arabic pronunciation, they ask about the Arabic that is preserved in the standard recitation of the Quran. This is a cultured pronunciation which often differs from the rapid speech dialects in that it pronounces the endings carefully; but more important to this discussion, it uses an `older' vowel repository than in modern dialects like, to take a random example, in Egyptian Arabic.
If you are interested in layla, the word for night, in this classical arabic, listen to the recitation of the 97th Sura `Al Qadr' from the Quran. You can find it in many places the web, May be http://www.searchtruth.com/chapter_display.php?chapter=97&translator=6 will help. The sura uses the word for night in sentences, so it has case markings -tu etc. at the end, but this discussion is more about the internal vowel which, in this case, is uninflected to my ear.
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