Comment on Common Issue: April 2015 fixes for SharePoint 2013 might not install on Sharepoint 2013 SP1 slipstream builds (updated May 12th) by Stefan Goßner

Hi Patrick,
that means that you did not install SP1 for for these language packs before installing April 2016 CU.
When reinstalling the language packs you have to install April CU again – otherwise these language packs will not be updated to April CU and you have an inconsistent patch level.
Cheers,
Stefan