(In reply to Petruta Horea [:phorea] from comment #0)
On Remote Settings STAGE, top-sites collection, the locales to be included/excluded are documented to use BCP47 format.
However, BCP 47 format is not recognized when setting some locales: for example RO locale, for which the BCP47 would be
ro-RO, the localized Firefox build being branded
ro-RO is valid according to BCP 47, so is
Afaik, we currently don't plan on using locale filtering. If we do at some point, it seems that we'll just have to know the exact locale strings being used in localized builds; it's not clear to me that something needs to change here.