Initial version of sphinx documentation and...

- remove ubuntu 21.04 from CI (end of life)
- adjust matrix strategy for clang.yml
- Use lessons learned from RetroArcher on localize.yml, crowdin.yml, and locale.py
- Add end of life comments to Dockerfiles
- Adjust dependency order in Dockerfiles

docs/source/contributing/localization.rst

@@ -0,0 +1,80 @@
+:github_url: https://github.com/SunshineStream/Sunshine/tree/nightly/docs/source/contributing/localization.rst
+
+Localization
+============
+Sunshine is being localized into various languages. The default language is `en` (English) and is highlighted green.
+
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=de&style=for-the-badge&query=%24.progress.0.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=green&label=en&style=for-the-badge&query=%24.progress.1.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=en-GB&style=for-the-badge&query=%24.progress.2.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=en-US&style=for-the-badge&query=%24.progress.3.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=es-ES&style=for-the-badge&query=%24.progress.4.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=fr&style=for-the-badge&query=%24.progress.5.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=it&style=for-the-badge&query=%24.progress.6.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+.. image:: https://img.shields.io/badge/dynamic/json?color=blue&label=ru&style=for-the-badge&query=%24.progress.7.data.translationProgress&url=https%3A%2F%2Fbadges.awesome-crowdin.com%2Fstats-15178612-503956.json
+
+Graph
+   .. image:: https://badges.awesome-crowdin.com/translation-15178612-503956.png
+
+CrowdIn
+-------
+The translations occur on
+`CrowdIn <https://crowdin.com/project/sunshinestream>`_. Feel free to contribute to localization there.
+Only elements of the API are planned to be translated.
+
+.. Note:: The rest API has not yet been implemented.
+
+Translations Basics
+   - The brand names `SunshineStream` and `Sunshine` should never be translated.
+   - Other brand names should never be translated.
+     Examples:
+
+       - AMD
+       - Nvidia
+
+CrowdIn Integration
+   How does it work?
+
+   When a change is made to sunshine source code, a workflow generates new translation templates
+   that get pushed to CrowdIn automatically.
+
+   When translations are updated on CrowdIn, a push gets made to the `l10n_nightly` branch and a PR is made against the
+   `nightly` branch. Once PR is merged, all updated translations are part of the project and will be included in the
+   next release.
+
+Extraction
+----------
+There should be minimal cases where strings need to be extracted from source code; however it may be necessary in some
+situations. For example if a system tray icon is added it should be localized as it is user interfacing.
+
+   - Wrap the string to be extracted in a function as shown.
+
+      .. code-block:: cpp
+
+         #include <boost/locale.hpp>
+         boost::locale::translate("Hello world!")
+
+.. Warning:: This is for information only. Contributors should never include manually updated template files, or
+   manually compiled language files in Pull Requests.
+
+Strings are automatically extracted from the code to the `locale/sunshine.po` template file. The generated file is
+used by CrowdIn to generate language specific template files. The file is generated using the
+`.github/workflows/localize.yml` workflow and is run on any push event into the `nightly` branch. Jobs are only run if
+any of the following paths are modified.
+
+   .. code-block:: yaml
+
+      - 'sunshine/**'
+
+When testing locally it may be desirable to manually extract, initialize, update, and compile strings. Python is
+required for this, along with the dependencies in the `./scripts/requirements.txt` file.
+
+   Extract, initialize, and update
+      .. code-block:: bash
+
+         python ./scripts/_locale.py --extract --init --update
+
+   Compile
+      .. code-block:: bash
+
+         python ./scripts/_locale.py --compile