Due to a quite old bug #0012860 storing 4-Byte-Characters to the Database lead to losing data since MySQL just stripped away all text after such a character. Therefore the ILIAS society funded a filter in the database-layer which filters those characters and replace them with a „?“. The filter is only applied when using 

- ilDBInterface::insert();

- ilDBInterface::update();

- ilDBInterface::manipulate();

- ilDBInterface::manipulateF();

- ilDBInterface::query();

- ilDBInterface::queryF();

This fix now has been published in 5.2, 5.3 and trunk. You get this information because there are slight interface-changes (added methods in ilDBInterface). 

For details please have a look at: https://github.com/ILIAS-eLearning/ILIAS/commit/609044a869c1cc4f1c91030ef8bcb1099982b730

This fix does not restore already corrupted data in the database since this is not possible.