This DTD appears to be used here:

https://searchfox.org/mozilla-central/rev/be7d1f2d52dd9474ca2df145190a817614c924e4/toolkit/profile/content/profileSelection.xhtml

Hey gandalf, Mossop mentioned that this might actually be kind of tricky because the last time he looked, Fluent isn't available before profile-before-change. Is that still true?

Hey gandalf, Mossop mentioned that this might actually be kind of tricky because the last time he looked, Fluent isn't available before profile-before-change. Is that still true?

How is it different from DTD? The API should be available but langpack selection may not be done at this point, which should match the DTD behavior. Am I missing something?

(In reply to Zibi Braniecki [:zbraniecki][:gandalf] from comment #2)

Hey gandalf, Mossop mentioned that this might actually be kind of tricky because the last time he looked, Fluent isn't available before profile-before-change. Is that still true?

How is it different from DTD? The API should be available but langpack selection may not be done at this point, which should match the DTD behavior. Am I missing something?

Last I checked locale registration hadn't happened before the profile was brought up, so even the built-in locale was not available.

I tested it by adding a <link rel="localization"/> to preferences.ftl and replacing one description with a data-l10n-id backed and it worked well, so I'd expect it to work on par with DTD!

Excellent, sounds like this bug is unblocked then. Thanks, gandalf!

https://hg.mozilla.org/mozilla-central/rev/44462bd32150

Verified fixed as part of PI 551; tested with Nightly 77 across platforms (Windows 10, macOS 10.15 and Ubuntu 18.04).