Google Cloud Translation API provides a simple programmatic interface for translating an arbitrary string into any supported language. Quick translate uses the API for translating missing locales. Google Translate API requires an authentication for pricing. More detailed information here.
Configure localization settings for Quick Translate
Create a text file in project assets and paste your API key into here. (Make sure that the copied key is correct one)
Google Cloud Auth File (Contains API key)
Open LocalizationSettings
Attach the created key file to Google Authentication File field.
Settings - Google Authentication File
Finally, you can translate missing locales automatically. See here.
If you want to use quick translate feature only in the Editor, exclude the auth file when deploying your game for production. For more information how to exclude an asset see here.
