Update git submodules
- Update extensions/VisualEditor from branch 'REL1_39' to b4e15af31018028b743f578793cbcbcd41522d7e
- Localisation updates from https://translatewiki.net.
Change-Id: I71676b2254bc17d9597e26d52b6c8abb5af37a7b
- Localisation updates from https://translatewiki.net.