Let's blame the Spanish.

Back home, in the land of 'milk and honey', there are bakeries.  Many of them produce some very lovely French baked goods.  Chief among these goodies is the croissant (or, as we say, kruh-sahnt).  <--Hey, at least we still don't say 'crescent roll'.

At the bread and cheese shop just around the corner from my house, I tried ordering a croissant, and was met with a bit of confusion.  The poor girl hadn't understood my (apparently shoddy) accent!  I hadn't known to say croissant (kwah-sah).  As I'm not in Strassbourg, I wouldn't have said it italicized anyway.

The first time I'd heard penchant spoken in a way that made me go, 'huh?' in the direction of the radio was just a few weeks back while ironing the hub's shirts.  The Beeb was broadcasting some such thing and this bit o' French popped out over the radio.  'Pen-effin-chant?!'  I could hear my dad's voice say in my head, 'Oh, reeeeeaaallly?' in that overly-comically-dramatic way that I think he'd nicked from the Jack Benny radio show of his youth.

I know the word, penchant.  We, too, have it in our version of English only we say it as: pen-shint.  Classy, ain't it?  We also have the words: original, royal, restaurant, cinema, and many more from Le Francais.  None of these words are pronounced avec une accent, if you catch my drift.  They've been a part of English so long, that they're, well, now just simply English.  So why the 'fancification' of penchant et croissant on this side of the world?

Well, it all started way back in the 11th century when the Normans invaded both England and its language.  After a few hundred years, English regained its primacy, but not without having been fundamentally changed by its French infusion.  Between now and then, I should think, that any trace of French-sounding words would have disappeared.  So, again, if the above French-derived words in bold aren't accented, then why are there a few that are?  (Is it perhaps because they entered the English language at a later date?)

I asked an acquaintance of mine, an Etonian, why he thought some borrowed words from French were pronounced en francais and some were not.  His answer was, in essence, this: because we, the English, have the ability to pronounce them so.  Hmmm.

Okay smarty-pants (this is my response to him in my head), if that were the case, then why can't a whole legion of people pronounce the word paella?  Hint: it don't rhyme with a cappella.  Or, for that matter, tortilla?
Or, even easier to say, taco?

"Taco" rhymes with "Paco"!

Can't remember Spanish vowels?  Just memorize this little ditty: A-E-I-O-U, mi burro sabe mas que tu!

The rain in Spain stays mainly in the plain!

 If the Spanish had invaded rather than the French, then, I suppose, we'd all have gotten the hang of the "ll" and "aeiou" sounds long ago.  Of course, we also might be ordering cafe con leche with our crescent rolls, too.