I don't have any sense that dash style is part of language use, whether English or any other. Of meeting some formal style prescriptions, okay, but not language qua language. Understanding is never -to my best knowledge anyway- dependent on the length of a dash. (Reading wiki's prescriptiveness about the various flavors of dash, I had to laugh. What on Earth do they do when writing something by hand? Or is that skill, along with good sense, lost to them?)

Oh, I distinguish between them too, Christophe -- but they're not part of language, they're just stylistic, like capitalisation. As German still does, 18th-c. writers in English capitalised nouns. The style changed so that nobody expects nouns to be capitalised in English these days, but the language was unchanged. The ability --and willingness-- to distinguish between dashes is similar: someone might be sneered at by stylistic pedants for not using the "proper" kind of dash, but few will notice, or care.

I like your third idea best: 2 tags. To formalise it, I've said so in an answer.

@MMacD Why would dash-style not be considered as much a part of the language as any other finer point of punctuation style?

@KyleStrand: Because, like capitalisation, they don't affect understanding. They might affect us on a social level, just as knowing or not knowing what fork to use at a formal dinner can affect how we're perceived by those who think such things are important, but the reality is that our ability to communicate is unaffected. Since which dash we use, or whether we use a dash at all, doesn't alter the meaning of what we're expressing, how can it be part of language rather than styling? And typographic styling at that!

@MMacD Well, because, presumably, different languages have different rules/guidelines/conventions for their usage. I would say that capitalization differences are also part of the language; German capitalization is different from English capitalization. And languages are nothing but social convention--every aspect of them, including these "merely" stylistic aspects, does impact "our ability to communicate."

How do you express caps and hyphens in speech?

@MMacD Do you consider the written word to not be part of a language??

Yes, I do. It's a representation of the language, but it's not the language. It's comparable to a map. Maps aren't the territory, they just represent it. Plenty people are illiterate in a language they know well, but you'll never find the opposite situation.

@MMacD You keep responding to me without @-notifying me, so I keep almost missing your responses. (Hence why my last comment took me a few days to post.) Anyway, yes, you will find the opposite situation; almost no one speaks Latin, but many people read and write it. Even for non-dead languages, I know people who, for example, find it easy enough to read and write languages that they have great difficulty speaking (for various reasons). And then there are languages such as Japanese with multiple writing systems with their own nuances.

You could consider written languages to be separate languages if you really wanted, but I honestly think it's absurd to say that they're "not languages".

@KyleStrand: (Sorry for not @-ing you! I'll try to do better) We understand written Latin because of its many descendants around the Med rim. If there were no such descendants, we'd be in the same position vis-á-vis Latin as we were with Ancient Egyptian before the Rosetta Stone. If you'd like a different example, try to decode Linear A, the Vinča texts, the Phaistos disc, or, for a lot of fun, the Harappan symbols. Nobody even knows whether the Harappan symbols represent a language as such, but they look as though a lot of energy went into creating them.

@MMacD I don't think my previous comment conflicts with your statement about how we know ancient Latin; I'm just saying that many people are literate in Latin but don't know how to speak it, which (as I understand it) is indeed the "opposite situation" that you were saying in your comment I'd "never find." I'm not sure what your point is about dead languages no one alive today understands.

@KyleStrand: I don't know of any evidence that any culture ever developed a written form of their language first, but there's lots of evidence of spoken languages that have no standard written representation. Scots and Low Saxon are two such. There's a literature in each one, but there's no orthography. The authors simply represent as best they can their own spoken dialect.

@KyleStrand: People who read Latin can also speak it, even if they don't do so in everyday life. That's true of every language that people can write. They might have lousy, unintelligible accents because they started learning the language in adulthood, but they can speak it.

"I don't know of any evidence that any culture ever developed a written form of their language first, but there's lots of evidence of spoken languages that have no standard written representation." Still not sure what that has to do with my original point that a written language is a language, either in the sense of being a separate language derived from an original spoken language, or in the sense of being simply a part of the original language.

@MMacD As someone who studied Latin, I'm going to go ahead and say that I disagree with the "can also speak it" assertion. I was well on my way to being a reasonably fluent translator when I lost the opportunity to continue taking Latin, but I was nowhere near being able to "speak" Latin. And I am aware of people who were taught written Latin without even being taught at all how pronunciation works!

I think my point might be that, while you can call a written representation a separate language, you'll get little support from linguists (or polyglots).

Your lack of ability to speak Latin to the standard you'd like doesn't impeach the idea that anyone who can write it can speak it.

The reason being that the Chomskian "deep structure" is the same for both spoken and written use, mutatis mutandis.

Latin is still, I believe, the official language of the RC church. I was raised RC, and the priests could certainly speak it back in the day, because they used it as a lingua franca.

@KyleStrand. Rats. I forgot again. Okay, this is just a ping, the content is above

@MMacD Thanks for the ping. Re: "support from linguists" -- perhaps the problem with this whole conversation is that neither of us is a linguist and neither of us has actually cited a linguist. If you have a source for the claim that linguists in general don't consider written languages to be "languages" (separate or not), I'd be interested in that. Otherwise, I suppose we could bring the question to Linguistics.SE.

But still-- whether or not you consider written language to be "a language", the original question was, does capitalization, punctuation, etc. belong on a site for English-language-learners? So, by extension, if the revised question is whether or not written English counts as part of the "English language", surely you would agree that most English-language-learners are probably interested in learning how to read and write in English in addition to how to speak it?

Or at least many?

....and that a site for people learning English is therefore an appropriate place to learn about how English is written as well as how it's spoken?

I just don't understand how any theoretical-linguistics argument could justify the assertion that learning a new language shouldn't include learning the written language; and from a pragmatic perspective, I don't understand why it would matter whether linguists consider written English to be part of "the English language."