Update git submodules
- Update extensions/CategoryTree from branch 'REL1_39' to 6cf9be873c4f93be159c7eb56bd03cf6a37efa16
- Localisation updates from https://translatewiki.net.
Change-Id: Ib5198cd7b10be5b0f3732cdb266e2d13c67cb3ea
- Localisation updates from https://translatewiki.net.