Merge branch 'stable-3.1' into 'move_to_junk'

# Conflicts:
#   interface/web/mail/lib/lang/ar_mail_user.lng
#   interface/web/mail/lib/lang/bg_mail_user.lng
#   interface/web/mail/lib/lang/cz_mail_user.lng
#   interface/web/mail/lib/lang/en_mail_user.lng
#   interface/web/mail/lib/lang/fi_mail_user.lng
#   interface/web/mail/lib/lang/hr_mail_user.lng
#   interface/web/mail/lib/lang/hu_mail_user.lng
#   interface/web/mail/lib/lang/id_mail_user.lng
#   interface/web/mail/lib/lang/it_mail_user.lng
#   interface/web/mail/lib/lang/ja_mail_user.lng
#   interface/web/mail/lib/lang/nl_mail_user.lng
#   interface/web/mail/lib/lang/pl_mail_user.lng
#   interface/web/mail/lib/lang/pt_mail_user.lng
#   interface/web/mail/lib/lang/ro_mail_user.lng
#   interface/web/mail/lib/lang/ru_mail_user.lng
#   interface/web/mail/lib/lang/se_mail_user.lng
#   interface/web/mail/lib/lang/sk_mail_user.lng