Does anybody happen to know the origin of the English iotated U sound? By this I mean the so-called “long U”, that has an initial y-glide when not preceded by a consonant, and palatalizes the preceding consonant in most dialects of English (e.g. “uniform”, “dew”, “Tuesday”). When did this first appear, and in what dialect? Do any other Low German languages have this?
Ok, yes, there may be another term for it but right now I have Russian on the brain, so that’s the terminology I’m using, as it seems to describe it pretty well. In several dialects (like my own) it behaves like a Russian Ю, with the y-glide and the palatalization. The way speakers of my dialect pronounce “dew” or “new” could very easily be written in Russian as “дю” or “ню”.
Sure, I just had no idea what it meant, and several online dictionaries crapped out on it too. Now at least I know what I’m ignorant of. 
It’s so annoying, this has been brought up many a time in my classes, but I just went through three separate textbooks and all I found was an excercise based on it. Assuming you’re talking about what I’m pretty sure you’re talking about, I can’t help you as to where it comes from, but there is some dialectal difference as to when this occurs.
Wikipedia’s take on this particular dialectal difference.
Actually, after flipping through yet another textbook, I can give you a bit of an idea. A Biography of the English Language (by C. M. Millward) indicates origins in Middle English diphthongs.
ME is Middle English, OE is Old English, ^ is the schwa I’m too lazy to code, and I left out all the macrons because I’ve had a long day. A little later …
PDE is Present Day English, and /j/ is what we usually spell as y.
So yeah, doesn’t look like it goes all the way back to the Germanic roots. Hope this helps.
– Dragonblink, linguistics grad student extraordinaire
Just wanted to note that Middle English was heavily influenced by Norman French, and in French the letter u is pronounced as a high rounded front vowel [y]. Like ü in German. When Russian transcribes Turkic words into Cyrillic, they represent this same vowel sound with the <yu> letter. Something about combining the [u} sound with palatalization/fronting.
I’m curious about this. In the dialects you’re thinking of, is dew pronounced the same as jew? Or is the palatalization more subtle?
Well, in my dialect (East Texas, leaning more towards the deep southern side of the equation), “dew” and “Jew” are distinct; the “J” in “Jew” is darker and more retroflex. It’s more of a “Dzhu” rather than a “d’yu”, if that makes any sense.