Update git submodules
- Update extensions/PageImages from branch 'REL1_39' to 78537e6a5442d993924c4e32ed1f4c2d21e40cab
- Localisation updates from https://translatewiki.net.
Change-Id: I54f0b5b8a097822794bea26c925057abf33dbb7b
- Localisation updates from https://translatewiki.net.