Weblate

Weblate is a libre web-based translation tool with tight version control integration. It provides two user interfaces, propagation of translations across components, quality checks and automatic linking to source files.
Stated goals.
Weblate aims to facilitate web based translation with tight Git integration for a wide range of file formats, helping translators contribute without knowledge of Git workflow.
Translations closely follow development, as they are hosted within the same repository as the source code.
There is no plan for heavy conflict resolution, as it is argued these should primarily handled on the Git side.
Project name.
The project's name is a portmanteau of words web and translate.
Notable uses.
These are some projects using Weblate: