Updated Russian translation for preferences.rpy.
Merge branch 'master' into i10n/zh_TW
i10n: Traditional Chinese language for launcher updated.
Document showif.
Merge pull request #481 from tlm-2501/patch-2

Updated Russian translation for preferences.rpy.
Merge pull request #482 from civalin/i10n/zh_TW

Traditional Chinese translation for launcher updated.
Remove translation TODOs.
Update changelog for 6.18.3.
changelog: Translation updates.
Link to translation best practices.
Add \[ as a way of escaping [.

This just replaces \[ with [[, which continues to work.

Fixes #489.
Do not predict labels that do not exist.

Fixes #491.