Update git submodules
- Update extensions/MultimediaViewer from branch 'REL1_40' to 18765d4a5a6d51df4c71420b931620ec8188e393
- Localisation updates from https://translatewiki.net.
Change-Id: I8c4222e225c7b3b25187e8ae4e55b1d23368788e
- Localisation updates from https://translatewiki.net.