> The en-dash and the em-dash are interchangeable in Finnish.

But not in English, where the en-dash is used to denote ranges.

I wonder whether ChatGPT and the like use more en dashes in Finnish, and whether this is seen as a sign that someone is using an LLM?

In casual English, both em and en dashes are typically typed as a hyphen because this is what’s available readily on the keyboard. Do you have en dashes on a Finnish keyboard?

> Do you have en dashes on a Finnish keyboard?

Unlikely. But Apple’s operating systems by default change characters to their correct typographic counterparts automatically. Personally, I type them myself: my muscle memory knows exactly which keys to press for — – “” ‘’ and more.

The main uses of the em-dash (set closed as separators of parts of sentences, with different semantics when single or paired) can be substituted in English with an en-dash set open. This is not ambiguous with the use of en-dash set closed for ranges, because of spacing. There are a few less common uses that an en-dash doesn’t substitute for, though.