That is probably on of the most confusing things about English. What do you mean "sounds like a vowel"? All vowels sound like vowels, what else would they sound like? While we're at the subject, why is Y not a vowel (except when it is) and why can you have more than one vowel in a syllable. In the example in the article they have unicorn, which is clearly spelled wrong if English were to make sense. The correct spelling should be "junicorn". Fixed.

Counting the number of syllables in a language like Danish means you just count the number of vowels. A syllable must have one, and only one, vowel. A word like "you", if it existed in Danish, would have three syllables, because all those letters are vowels, at any point in time.