Silent vowels~ These are not really like English. And in all cases they are not silent. Generally this rule comes into affect when someone is trying to sound more natural. Although I do think much of it is just caught from hearing the language.
Hehe I guess I'll never stop saying my personal opinion here xDWell I'm sure you all know those phrase books right? Well i really hate it when they leave about vowels that should be there in the words. I dont feel that thats good because people wont know the correct spelling.
It's common for most people to know about dropping the "u" off of "desu です" how ever that's not always the case. Hehe there is not much for rules I can actually tell you. Just be aware. If people try to act on some of the rules they hear they often end up sounding unnatural and mess up. I've heard a lot of bad Japanese from people in my class.
Hmm I should think of some sorta examples xD hehe but these are not solid rules.
So often for "Desu です" its pronounce "des" though there is no way to express this in kana. I guess you can drop the "u" mostly when desu is at the end of the sentence with nothing more after it. but when you add "yo よ" or "ne ね” or something after desu, you dont drop the "u".
Lets move a step forward. For ex the word "suki すき" the "u" after su す, so u just make a "s" sound then "ki き" as in "ski" xD lol actually its very similar to the American word "ski".
Though just because the "u" is dropped in this case does not mean it is dropped in all cases.
Next is "shi し", "shigoto しごと" "shikashi しかし” in the 1st example you say the entire "shi し" however in the 2nd example the "shi し" is pronounced as "sh". hehe i should make a vid for this huh xD.
Next is "ku く” as for this as well the "u" can be said or not said depending on the word. For ex. "Kuroi くろい", "watakushi わたくし" as I'm sure you can guess from me saying it 100 times, the 1st example you say the full " ku く" and the 2nd its just "k". わたくし is just a formal version of わたし, if anyone wonders.