Go through the Translator’s Handbook to learn how to contribute to WordPress by translation. From this handbook, you will learn more about the Polyglots team, how to translate WordPress plugins, themes, meta sites, and apps, and what best practices you need to follow.
You can also take the Polyglots Contributor Training course, which will help you go through the process of becoming a Polyglots team contributor. This course will help you to understand how WordPress translations work, what a glossary & style guide is, and much more.