Sorry about the mushy images, I must have got the size wrong or implored the wrong gods or something… If you View Image they’re crisp, FWIW.

A tad more logical but more out of random preference I would probably use the singles too. There is the “semantic use” of single quotation marks for emphasize or to highlight explanations for things that aren’t quotes. But that case doesn’t really apply here, or does it? I don’t know of any “rules” for such a case. Typesetting guidelines are more about helpful conventions than rules anyway, so just do what you think will be understood most easily by the reader.

Right now I don’t even know what’s more easily understood by me… thanks, Indra.

(And no, the semantic differentiation of singles for things like technical terms or titles that aren’t really “speech” does not apply here. Fortunately we don’t have any such standalone single quotes in this book.)

{To Follow}

Nina, your logic makes more sense to me, but in those images that dash looks so slight that the relatively showy normal (double) guillemets threaten to jump out of the hierarchy to my eyes, which might push me towards using the single ones.

I'd agree with Craig, those dashes could do with being more prominent, whichever way you decide to go. To my mind, if you're using double ones in the surrounding non-dialogue text, I'd say it's more consistent to stick to one variant, the double, throughout, rather than have double in text and single in dialogue.

Thinking as an editor, I would agree with your typographic logic: single guillemets indicate nesting within guillemets, not nesting within discourse. Thinking as a typesetter, I would prefer em-dashes rather than en-dashes for the dialogue, if possible. But my opinions are very Anglophone; I don't really know how German-speakers perceive these things.

Thanks all so far.

On the dashes, I agree (and realize) that they’re relatively short, but in this/our German/Swiss context this is actually quite welcome – em-dashes would definitely be over the top. Craig’s point on what that means for the visual hierarchy with the guillemets does give me pause though… hmm.

What’s interesting is that Frode (or whoever is handling the Monokrom account) has commented on Twitter that double guillemets would be commonly used with the dashes in Norwegian (which uses both dashes and guillemets) – so there’s a precedent.

I’ll see the editor today & we’ll have a (presumably final) talk about it :)

That was me yes. En dashes and guillemets would be used in Norwegian. Since you are not typesetting a Norwegian book, and doing something entirely new, you are probably free to define something else.

Dramatic change of perspective: We have changed all guillemets in the text – within direct speech or no – to single ones :)

Upon further inspection of what actually is inside those quotes (thanks for this question on Twitter, Frode), we (editor + I) realized they’re all book titles, names of restaurants and other such things that can easily be quoted in single guillemets as well. Changing them to singles also makes them less loud visually (thanks for that, Craig), makes them not feel weird inside direct speech (where most readers will be used to seeing single ones) while still maintaining consistency between quoted and not quoted text (as I wanted it).

Ergo, everyone happy, problem solved. Thanks, all!

Single guillemets?
I'm sure your solution wasn't as sophisticated as this one:

hhp

We have changed all guillemets in the text – within direct speech or not – to single ones

like!

In the case of book titles, names etc … As long as the language is not German, these might already stand out enough because they usually are written with initial caps. When that does not stand out enough, you could also consider to write them in italics (as long as that does not conflict with other uses of italic within the document)

It's probably too late, but in Sweden it'd also be double quotation marks within a dash-indicated direct speech passage. But then we hardly use quotations marks at all, except when quoting text or as scare quotes. Possibly for song titles.

Sounds good (and interesting, even if too late for this specific case).

Albert-Jan: The language was German in this case… :-)

Thanks again for all the input!