Support Additional Sources for Translation Pulls

Summary:
Currently, the translation pull functionality supports only public GitHub repositories. This works well for many open-source projects but creates limitations when working with other version control systems or private repositories.

Use Case:
At RaccoonGang, we primarily use GitLab. As a result, we’re unable to leverage the existing translation pull mechanism without workarounds.

Proposal:
We’d like to explore extending the functionality to support additional sources for pulling translations, such as:

• GitLab (public and private)
• Private GitHub repositories (with authentication)
• Potentially other VCS platforms (Bitbucket, etc.)

We believe this would make the tool more flexible and broadly usable for diverse setups.

To address this, I'm preparing a pull request with a proposed implementation and would appreciate feedback on the approach once submitted.
Let me know if this aligns with the project direction—we're happy to iterate based on your input.

Start by locating the translation pull functionality and reviewing how it currently obtains translations from public GitHub repositories. Clarify the supported additional sources and authentication requirements, then verify the result with source-specific translation pull scenarios.