GitHub uses Linguist to detect languages, see the “Adding a language” section in the Linguist contributing guidelines:

  <a href="https://github.com/github/linguist/blob/971e152fabca12e0ad386833eecb7b15e312a09f/CONTRIBUTING.md#adding-a-language" target="_blank" rel="noopener">github.com</a>

github/linguist/blob/971e152fabca12e0ad386833eecb7b15e312a09f/CONTRIBUTING.md#adding-a-language

<pre><code class="lang-md"># Contributing

Hi there!
We're thrilled that you'd like to contribute to this project.
Your help is essential for keeping it great.

Contributions to this project are released to the public under the project's open source license.

This project adheres to the Contributor Covenant Code of Conduct.
By participating, you are expected to uphold this code.

The majority of contributions won't need to touch any Ruby code at all.

Dependencies

Linguist is a Ruby library so you will need a recent version of Ruby installed.
There are known problems with the macOS/XCode supplied version of Ruby that causes problems installing some of the dependencies.
Accordingly, we highly recommend you install a version of Ruby using Homebrew, rbenv, rvm, ruby-build, asdf or other packaging system, before attempting to install Linguist and the dependencies.

Linguist uses the charlock_holmes character encoding detection library which in turn uses ICU, and the libgit2 bindings for Ruby provided by rugged.

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