I just noticed an error in the german language file plg_jem_mailer.ini which causes the file not to be loaded:
on line 200
PLG_JEM_MAILER_LOG_SEND_ERROR="Fehler beim Senden einer Emails an "_QQ_"%s"_QQ_"_QQ_
at the end "_QQ_ has to be removed in order to work (compared to the english version)
This bug may be due to strange Transifex behavior
This message is used only in logging as far as i can see in the code.
You have turn on Joomla Debugging (see here
) and you have to set the debug plugin to log almost everything. Then change an email adress to a wrong adress and book an event this user.
I have used your PLG_JEM_MAILER_LOG_SEND_ERROR in my german language file and it worked
from the log file: