Update git submodules
- Update extensions/Math from branch 'REL1_39' to f6e18c708da41dd8e6a6da68086179e2a8433f64
- Localisation updates from https://translatewiki.net.
Change-Id: I378ad8b834ba7129dec50458ab02582b1cc2fc57
- Localisation updates from https://translatewiki.net.