I live and work in a country where the language is not English at a company that does not permit me to download and install software at will. The version of Firefox Developer that is available is therefore not in English, and I am unable to download a different version. In plain old Firefox I can install language packs to change the interface. Will that functionality be introduced in developer edition?
Found a relevant thread at https://www.reddit.com/r/firefox/comments/7b48w1/is_there_a_way_to_install_language_pack_on_beta/
Currently langpacks only work for a given version of Firefox, and (I think) are only available up to the Release channel.
According to the thread linked above, something is in the works to improve that for beta/nightly (and surely DevEdition as well). Maybe @_flod can share more details about that?
Language packs are actually available for each version, but they’re not available on AMO, and pretty hidden on FTP.
Example, for 58 Beta:
I don’t know if Developer Edition is available on FTP? I couldn’t find any folder at a first glance.
As for future improvement, right now the priority is to switch the localization infrastructure to Fluent, that will give us space and tools to improve and add features (runtime fallback to different locales, localization updates separated from code, multilocale builds). The latter might be the actual solution for this kind of issues.
DevEdition is currently at version 58.0b4, same as beta. So the xpi linked above should work.