Summary
The action emails, such as Request payment email, Request payment method email and so on, can be sent in a different language than what is set as the default language for the customer.
You would see the option to change the locale in the preview of the action email template as in the screenshot below. All the language enabled in your site will be listed for you to choose from.
Related articles and Documentation
How to configure multiple languages in Chargebee.
Default and Non-default languages.