system language leak via reply: Changed reply_header behaviour (upstream) requires setting new preference
We used to set
mailnews.reply_header_authorwrote = %sto prevent the disclosure of the system language.
With Thunderbird 31 and later this pref is deprecated and does not work anymore. https://bugzilla.mozilla.org/show_bug.cgi?id=1009585
New pref/fix:
mailnews.reply_header_authorwrotesingle = #1:
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information