[localization] Create a place on this repo to capture best practices

As different teams identify localization best practices, let's capture them in a "Localization Best Practices" doc that can live under LOCALIZATION.md.

It should include different workflows to handle various localization aspects, such as:

- How to keep track of outdated content
- How to keep track of updates in the English Glossary

...and much more. @seokho-son, what other workflows have we converted in the past that should be added to this list?

cc @huats

Start by inspecting LOCALIZATION.md and the repository's existing localization guidance. Gather the workflows mentioned in the issue, including tracking outdated content and English Glossary updates, and clarify which additional past workflows belong in the document. Done means a coherent Localization Best Practices document captures the agreed workflows.

Written by the indexing model from the issue text.