nit: label.  Less-nit, since https://developer.mozilla.org/en-US/docs/Mozilla/Localization/Localization_best_practices#Add_localization_notes goes to effort to document the localization note syntax and call it out as important, let's start the trend of more properly doing:
```# LOCALIZATION NOTE(settings-account-play-sound-onsend): ```
as it proposes.

(My bad for not starting us off with that originally; I assumed that the tools were not horrible and that the annoying boilerplate was just cargo culting, but it sounds like it's not.)