Current state

Currently we use a logger which i completely bound to phpBB, which leads to a few issue:

but it also has some nice features like:

there is also some other feature that, I think, shouldn't exists like:

The ability to delete all or part of the logs, I think that it should be done by a cron job and nothing else (ie: just automatic purge) or at least with a special admin permission

Proposal

Our logger must be PSR3 compatible
Use an interface to be able to change the logger
Use Monolog if available and backport the Symfony Monolog Bridge and Bundle (their integration is pretty good: they use Monolog and its features if available, but their still able to use any logger which implements their interface without having to change anything else than the definition of the logger service)
Use a custom handler to store some entries (or all of them I don't know?) in the database (mainly what is currently logged) and so keep our abilities to display and filter the logs
Improve the current UI to add the severity
Write all the logs in a file and rotate them (ie: one file per day) by default, they will be written in the board default language
Use the DI and a config file (DI extension) to manage all the configuration, so the board admin will be completely able to configure the logging
Add a viewer for the log files in the acp?