Change how supported locales for composer attribution language are detected
org.gnome.evolution.mail.composer-attribution-language by default uses an empty string, which means to use the same language as the user interface.
The GUI setting Preferences >> Composer Preferences >> Replies and Forwards >> Language always only shows Same as user interface with no other language to choose from, and does not reflect what is set in
composer-attribution-language, although the setting of
composer-attribution-language is actually honored if set using
dconf-editor (tested by launching Evolution with the user interface language de_AT and
composer-attribution-language set to en_US and vice versa).
It's the same for the Accounts Editor, which always only shows Use global default as language setting in the Compose Messages tab with no other language to choose from.
The Replies and Forwards Language really should be configurable from the GUI, at least globally from the Preferences menu, but better individually for each mail account and ideally for each individual reply and forward, because the current situation makes this totally impractical when replying to and forwarding emails in more than one language.
I am using Evolution with German as user interface language, but I reply to and forward emails in German and English, so every time I do it in English it has the quotation string (
composer-message-attribution) in the wrong language because it is always only applied in German in my case.