Dialect "rules" and the pronunciation of individual words
Consider an American actor who is tasked with mastering British Received Pronunciation for an upcoming role. If he has a talent for vocal mimicry, as many actors do, he should have no trouble picking up the "rules" of RP just from listening to people speak it: the non-rhotacism of the dialect, the aspiration of intervocalic t, the characteristic intonation patterns and prosody of RP, and so on. For the most part, he should have no trouble speaking RP like a native. Yet he would never in a million years figure out on his own that lieutenant should be pronounced "leftenant," for example, or that controversy is often pronounced with the accent on the second syllable, unless he hears those specific words pronounced. To my knowledge, there are no general characteristics of RP that account for the mysterious appearance of an f in lieutenant (or, if you prefer, there are no general characteristics of General American that account for its absence). You just have to know how those specific words should be pronounced, because you'll never figure it out on your own.
Do linguists recognize a distinction between the "rules" of a dialect on the one hand and its individual pronunciation "quirks" on the other? Is there a term for this phenomenon? Is it considered merely a variation on regional preferences for certain words over their synonyms (e.g., rubbish vs. garbage), or is there something else at play here?
(Disclaimer: I take no position on whether the BE or AE pronunciation of any of these words should be considered the "quirky" one; I simply note that one couldn't easily intuit one pronunciation just from knowing the other.)
Solution 1:
Do linguists recognize a distinction between the "rules" of a dialect on the one hand and its individual pronunciation "quirks" on the other? Is there a term for this phenomenon? Is it considered merely a variation on regional preferences for certain words over their synonyms (e.g., rubbish vs. garbage), or is there something else at play here?
I would say that linguists in general tend to consider the entire lexicon of each language/dialect/sociolect/regiolect/idiolect as a more or less complete system unto itself. This system may share or not share more or fewer characteristics with other like systems, but they are ultimately separately existing systems.
These systems are all basically phonetically based, though. Writing complicates matters, but it doesn’t change the basics of the systems: they are at their inmost based on spoken sounds.
As an American, you can learn to pick up RP quite easily to the extent that RP mirrors American phonemically. If the underlying phonemes of a word are the same, a simple translation or transposition from one phoneme-based system to another is all that is needed. But in any case where the underlying phonemic structure differs, there is no other way than just to learn by rote. Lieutenant is one such word: it is simply ‘sound-spelt’ differently in the two dialects. The fact that the codified and standardised conventions of our writing system has them spelt the same way makes it less obvious to draw this conclusion, but American and British ‘lieutenant’ are really two different words, just like ‘truck’ and ‘lorry’ are. Of course, it is easier to remember in a practical situation that a word for something in a foreign system is almost, but not quite, the same as in your own system, so there is a cognitive difference. But as far as direct transposition from system to system goes, there is no difference: something is either mappable or it isn’t.
I don’t think there is really a term for this, except perhaps in the guise of pointing out that words that aren’t mappable constitute isoglosses between the systems (which isn’t really what you’re looking for). With all related languages, there are words that map perfectly between systems, and there are words that don’t—the latter category being made up of words that, once you know them, can be retrofitted into almost mapping, and words that do not match at all. But for all languages, this is a continuum.
Between American and British English, the vast majority of the language maps, and a minority of words don’t. Between languages like Spanish and Portuguese or Ukrainian and Russian, a good percentage of the words map, but many don’t. Between Danish and German, a fair few roots are mappable, but the majority of the morphology—and hence of the complete surface forms of words—are not. Between Icelandic and Dutch, virtually nothing is mappable, though many words still fall in the ‘lieutenant’ category of words that are close enough to be recognised as being related to each other. And between Greek and Swahili, virtually everything is neither mappable nor recognisable.
Solution 2:
In general, the broadest term for speech varieties is "dialect" (and it's infamously difficult to draw a line between "dialects" and "languages").
A more specific term is "accent". Ben Trawick-Smith explains in this blog post "Dialect vs. Accent" that accent only covers pronunciation features, not grammar.
I'm actually not sure if sporadic word-level features like you describe here would technically be classified as part of "accent". Anthea Fraser Gupta on Linguist List says "An accent is a way of pronouncing a language" but it's not clear to me if this includes details about the pronunciation of individual words. Another presentation I found says "An accent is a certain form of a language spoken by a subgroup of speakers of that language which is defined by phonological features." I'm not sure if the word lieutenant having /f/ is exactly a phonological feature of British English, although it's certainly a phonological fact.
I think a term that would clearly exclude single-word pronunciation differences like "lieutenant" is "sound system". That "lieutenant" has /f/ is clearly not a feature of the British English sound system, because it is not part of any systematic difference between British and American English.
There are other changes that are clearly part of systematic differences between British English and American English. The most obvious differences between the British English and American English sound systems are related to phonemic inventory and phonotactics.
The phonemic inventory of "Received Pronunciation" contains sounds like /ɪə̯/ and /ɒ/ that do not exist in the "General American" phonemic inventory.
American English phonotactics allows /r/ to occur before a consonant, while Received Pronunciation phonotactics do not allow this. But on the other hand, Received Pronunciation allows the sequence /njuː/ to occur word-initially while most varieties of American English do not. (Dropping /j/ in these contexts is not really a feature of "General American" as it is usually defined, but it is a sound change that is much more common in the United States than in Britain.)
However, only some sound changes affect phonemic inventory or phonotactics. The British English "trap-bath" split for example didn't create any new phonemes or (as far as I know) set up any phonotactic patterns that don't exist in American English. But it causes a difference in the distribution of phonemes in certain words. I think most people would consider this sound change to be part of a "British accent", but it isn't actually completely predictable, so an American would have to memorize which words it affects.