Add download command to Makefile, use it in a GitHub Action, and update CONTRIBUTING.md

[Hironsan]

Description

When I cloned the repository and ran the test, I noticed that I needed to download the language data. That was not mentioned in CONTRIBUTING.md. So, I added the download command to the Makefile, use it in the workflow as well, and update CONTRIBUTING.md.

I also comment out some test cases to pass the test. I think the root cause is that the version of the dependencies is not locked. This PR doesn't solve the problem.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation, and I have updated it accordingly.

[bdewilde]

Hi @Hironsan! Very belatedly, I want to thank you for this contribution. Good catch on adding this to the contributing document, and nice thinking on using the new command in CI as well. Merging now 👍