From https://hg.mozilla.org/comm-central/rev/a7826463e5c2

The above changed some strings, but only half way. Fluent doesn't use variables like that, so if you change value of a reference all of the new key must change, not only what it refers too. I think in short, avoid using them :/

https://hg.mozilla.org/comm-central/rev/a7826463e5c2#l5.14 and https://hg.mozilla.org/comm-central/rev/a7826463e5c2#l5.76 - for this, spaces-pinned-button-menuitem-mail would have had to change to spaces-pinned-button-menuitem-mail2 (or something), not only the one attribute.

I got a complaint that French localization for this is missing, which is what prompted the investigation. Indeed it's the old values for the wrong refs. https://searchfox.org/l10n/source/fr/mail/messenger/messenger.ftl#195,233

Will it require further work on the part of localizers? Or is this just a technical change?

Localizers won't currently notice they need to localize. For users, the reference name (literally "{spaces-toolbar-button-tasks.title}") will show instead of the value.

I'm not sure about what the best fix is. Probably need to update all the main strings that use any of the references that were updated.

Same thing for starMessageButton.

message-header-msg-not-flagged .aria-label is not filled (for French, Dutch).

Argh, this is horrible, sorry about that.
It's weird that this issue doesn't appear for non-localized versions but only for localized strings.

I will update the ID of all the strings that use the updated reference, hoping this will fix it and won't require extra work to localizers.

(In reply to adrien.rybarczyk from comment #3)

Same thing for starMessageButton.

message-header-msg-not-flagged .aria-label is not filled (for French, Dutch).

Indeed, from bug 1556261 - https://hg.mozilla.org/comm-central/rev/9e43bc3f94ec - can't add a property without changing the key. Localizers won't find out about that.
Alex, do you want another bug for that, or?

That aria-label is also kinda wrong.
I think we can deal with it in bug 1775296

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/6e849249b8e1
Fix wrong fluent IDs for the Spaces Toolbar Pin button. r=mkmelin

Comment on attachment 9282246 [details]
Bug 1775273 - Fix wrong fluent IDs for the Spaces Toolbar Pin button. r=mkmelin

[Approval Request Comment]
Regression caused by (bug #): bug 1665511
User impact if declined: Missing strings for localized versions
Testing completed (on c-c, etc.): on c-c
Risk to taking this patch (and alternatives if risky): it should be low, even tho fluent IDs have changed, the reference to an existing fluent string shouldn't cause problems. I think...

Comment on attachment 9282246 [details]
Bug 1775273 - Fix wrong fluent IDs for the Spaces Toolbar Pin button. r=mkmelin

[Triage Comment]
Approved for esr102

Thunderbird 102.0:
https://hg.mozilla.org/releases/comm-esr102/rev/b752f47043c2

Very few locales have those strings:

https://searchfox.org/l10n/search?q=spaces-pinned-button-menuitem-mail2&path=&case=false

(In reply to Magnus Melin [:mkmelin] from comment #0)

The above changed some strings, but only half way. Fluent doesn't use variables like that, so if you change value of a reference all of the new key must change, not only what it refers too. I think in short, avoid using them :/

https://firefox-source-docs.mozilla.org/l10n/fluent/review.html#message-references