Update git submodules
- Update extensions/WikiEditor from branch 'REL1_39' to 18b6c81e65621ac220b11bd07a7a708ac249836a
- Localisation updates from https://translatewiki.net.
Change-Id: I58f24c90f70a7de5087b458385943769a4b8b028
- Localisation updates from https://translatewiki.net.