> Regarding the link, I was more thinking about how your system handles the some.introductory.paragraph translation and how you differentiate between potential HTML in the translation vs HTML in the click_here variable vs HTML in another potential variable containing user input.

Well, the differentiation is between strings which are dev-authored and parsed during compilation/boot time – which are trusted (untainted) and thus may contain HTML that's rendered directly – and tainted strings which come in at runtime either from user input or from via the translations lookup (among other things), and which can never be rendered without fully HTML escaping (without the code explicitly untainting them, at least, but that would never survive code review because it's profoundly unsafe to do this).

click_here isn't a "real" variable in the source language, it's just something that the translation API can replace during the translation load. To the extent that it can contain HTML, it can do so if and only if it is bound to an untainted string instance during the translation load – binding it to a tainted instance would cause any HTML that gets inserted into there to get fully escaped. "link" being dev-controlled produces untainted strings, but might itself consume a tainted string for its title (and thus escape that while rendering the title as part of outputing its untainted string), etc.

> how you differentiate between potential HTML in the translation

it's very simple: the translation is not trusted and thus can't contain HTML that gets rendered without being fully escaped, and thus looking like garbage. If you really wanted to style something in the middle of the paragraph (which again, effectively never really comes up in my experience) you would have to split the paragraph into 3 keys: everything leading up to the start of a tag, whatever's inside the tag, and everything after the tag.