Update git submodules
- Update extensions/Math from branch 'REL1_39' to dc39892f46f807d3e9ed4bbc4df5342fc4bb4869
- Localisation updates from https://translatewiki.net.
Change-Id: I1d3e150b5e4a69b38a301bddadc0984052656f57
- Localisation updates from https://translatewiki.net.