It generates the code I expect, but the approach was wrong, because if a translated string contains HTML-unsafe characters, things will break. Moving back to <%- ... %>.

Okay, so let's talk inline localization and escaping. I've been going back and forth on this for a couple days (wrote up stuff in Notion and.. there's just trade-offs).
So, we have the following two approaches we can take:

// Using <%- ... %> and wrapping in quotes
const s = _.template(dedent`
    <p>
     <%- "${_`This is some text to localize, which requires escaping \\" or ', depending on the wrapping quotes.`}" %>
    </p>
`);

// Not using `<%` of any form, but manually calling _.escape:
const s = _.template(dedent`
    <p>
     ${_.escape(_`This is some text to localize, which freely allows " or '.`)}
    </p>
`);


This is (very roughly) equivalent to the following:

const s = _.template('<p><%- "' + gettext(...) + '" %></p>');

const s = _.template('<p>' + _.escape(gettext(...)) + '</p>');


You can see how the former, while less verbose, requires us to consider what sort of quoting we have in the message, and this could pose issues. This is because <%- requires a value (string in our case), and we can't just append a string (the gettext call) to it, since that'll otherwise look something like <%- This is some text to localize.... %>, so we have to quote.
The latter is more verbose, a bit uglier, but avoids the issue by building an escaped string and concatening it, rather than passing it in to a <% tag.
I'm leaning toward us using the latter for now, since it's safer and less constricting. We could add some syntactic sugar through another plugin at some point maybe... I don't know.
What do you think?