There is a global phenomenon where the sound [l] is pronounced like a vowel, known as l-vocalisation. We do it in English, where the word ‘fall’ would sound a bit more like ‘faw’ in certain dialects like cockney or estuary English.
The French used to do it too, which is how they got from the Old French ‘bel’, meaning beautiful, to the Modern French ‘beau’, which came about from the [l] in ‘bel’ sounding more like a [w]. This explains how the masculine ‘beau’ sounds so different to the feminine ‘belle’.
L-vocalisation happens in Bulgarian too. It occurred in Old French because it came after a vowel at the end of a word, while the reasons in Bulgarian are more social than phonological.
In Bulgarian, [l] is pronounced more like [w] or [o] in informal/young and hip contexts, for example the word [malko] would be pronounced more like [maoko].
Since l-vocalisation happens with Bulgarian youths and a lot of London accents in the UK, you could say that it essentially acts as a passport for a Brit to sound young and cool in Bulgaria and vice-versa.
-Natalie