OK - I've waited long enough...

WOW -"Has anyone else noticed that each language has it's own musicality? Rhythm if you will? - You bet! Aligning lyrics to music, just one of my favourite endeavors, is filled with the discovery of what is musical about language - both rhythmically and melodically. (Of course this says nothing about the effect of music on meaning after doing so!)

"Any singers among us who perhaps have had similar problems with American or English lyrics translated into another language?" - I have very little experience with translating from English, however, translating to English always leaves certain 'holes' for which there is no word(s) to 'fill'. I would imagine it is the same the other way around. In performance, as well as analysis, music seems to be dictating (to a certain degree) how successful a language communicates through it as well as each language seemingly dictating (to a certain degree) what music will be best at not obfuscating its intent. (ps. I assume by "Tempo C" you mean 'common time' or 4/4 (ie. "Time Signature")

"...no two hearers get exactly the same message" I'll save this one for another time

There is no doubt that composers work within a certain "sonic comfort" which their "mother tongue" has embedded into the way they hear (and listen). This is one of the obvious ways language exposes its own musicality. Actually (tsuwm-registered trademark), there is nothing obvious about it... except most people I know who know very little about music theory, per se, will guess correctly the "nationality of a composition"; just as they can do with the "nationality of a language", yet not understand a word of it.

In formal English, the rhythm patterns formed by the words, and intonation, or the rise and fall in pitch by the speaker, as well as the speed and volume, and the deliberate use of silence for contrast, all can be as complicated as a Bach work. - I'll do my best to leave Bach's "supposed complexities" out of this (for personal reasons)... I agree completely with your post, especially when it comes to the intentional use of silence (one of the key ingredients to communication). I mark up my poetry/prose for accurate performance, just as I would a musical score, and it does make a big difference!

"And what is the scansion of a 11 syllable line of a Petrarchan sonnet?..." - I guess I don't have a direct answer to your question... but from my experience... when rhythmic structures become large enough (ie. span a significant length) they naturally become a combination of smaller structures... "naturally" of course meaning "functionally" in this context, whereas, in a context of meaning, longer structures will be required to be successful.

[heavy breathing end of rant emoticon]