Go through Translator’s Handbook to learn how to contribute to WordPress by translation. From this handbook, you will learn more about Polyglots team, how to translate WordPress, plugins, themes, meta sites, apps and what best practises you need to follow.

You can also take Polyglots Contributor Training course which will help you go through process of becoming Polyglots team contributor. This course will help you to understand how WordPress translations works, what is glossary & style guide and much more.