I have upgraded to the version 4.7.16 (Joomla, Windows10). After the upgrade I installed from github the extension l10n_update.
I get now rmessages from l10n_update "Cannot read unrecognized property CRM_Core_Config::$gettextResourceDir."
Is this extension still in use? I have found it on github, after I read about it on the wiki as recommended for the translations. The property is used in the extension, but in the documentation it is marked als removed.
On the page https://wiki.civicrm.org/confluence/display/CRMDOC/Extensions#Extensions-Joomla
the default location is <docroot>/media/civicrm/custom_ext. I think it must be <docroot>/media/civicrm/ext. That value is the default location in the application and that directory is present. But the installation of l10n_update was no problem.