Update git submodules
- Update extensions/Math from branch 'REL1_39' to 2768227a6674eab3a7e3db14862dca1427ffd9f6
- Localisation updates from https://translatewiki.net.
Change-Id: I470b5791ec7f86ffd7385f036253ac9f9839ca72
- Localisation updates from https://translatewiki.net.