I have noticed that all dictionaries on AMO have been converted to WebExtensions. I have updated our build scripts for Czech spell check dictionary add-ons but I also got feedback that the new format does not work well when there are two dictionaries installed for the same locale. In our case (cs) we have two add-ons (with and without diacritics).
Does the keys of the “dictionaries” property in manifest.json have to be valid ISO locale codes, or they can be anything? If they have to be valid ISO code, how can Firefox handle multiple dictionaries with the same code?