Handle diagnostics customization on the fluent side (for one specific diagnostic)

[oli-obk]

r? @davidtwco

[rustbot]

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[davidtwco]

I'm a little hesitant about adding functions like this - on the one hand, it reduces duplication we're seeing where a ty_is_static-esque field is added to branch on in the Fluent code, which just feels yucky when the ty field is there (similarly with opt_is_some fields). On the other hand, I don't know how this will look for translators and whether they'll know they need to branch like this to translate the entire error.

[davidtwco]

@bors r+

[bors]

📌 Commit 64e5f91 has been approved by davidtwco

It is now in the queue for this repository.

[est31]

I wonder where these functions should be documented, because there should be some documentation of them somewhere.

I think for translators of some piece of software, or even some document, the benchmark should always be: does the person, in addition to speaking both languages, understand what they are translating? A lot of words are jargon, e.g. the words that collins dictionary suggests for "compilation" are all wrong, "Zusammenstellung"/"Abfassung"/"Sammlung" are all not correct ("Übersetzung" is the correct translation, or the loanword). Similarly, binary can either be translated as "binär" or as "Binärdatei" depending on whether you mean the noun or the adjective. As an example of what happens when you don't know jargon, you can see what Google's non-human translator API has done to their Android documentation: they translate "Android Rust patterns" as "Android Rostmuster", and "Example C binary" as "Beispiel C binär".

So I think it should be safe to assume some capability for programming from translators, and thus, to use stuff like STREQ. But even people who know programming enjoy a specification of the functions available to them :).