Weblate

As a software developer, I really love Weblate. It allows my users to translate my program, so all I need to do is pull the changes in using git.

As far as I have researched, it is the best free and open-source collaborative translation system available. The alterative open-source tools like Pootle and Zanata didn't seem to have any hosted options (and either way both appear to be discontinued). So Weblate seems to be all we have.

The official hosted Weblate instance is free for open-source projects, and I highly recommend click around the website: https://hosted.weblate.org/

Basically you add your "project" (let's call it MyVideoGame) which can contain multiple "components" (let's call them "LevelOne", "LevelTwo"). These components can map to a file in your source code repository (let's say it's hosted on GitHub) using a pattern match (like let's say "/path/to/component/*.po"). You can configure Weblate to push the changes back to GitHub in various ways, or just synchronize it manually.

By the way, I highly recommend encouraging your translators to log in: translators who are not logged into Weblate can only "suggest" translations (which needs to be accepted by a logged in user). Logged in users can also see a large number of "Automatic Suggestions" from machine translation services like DeepL, Google Translate, Bing Translate etc, which may save time. Also it really helps track who's making changes when multiple people are translating together.

Also there are a bunch of configuration options available in the Settings page, and Add-ons pages.

The Weblate user-interface could probably be improved over time, but it's definitely a solid program. Remember, Weblate is an open-source project so please suggest to them any improvements. In my experience they have been very fast to reply to my enhancement suggestions on GitHub.

Hopefully they are getting a large number of paid applications using their platform too, because I really love the tool! :)