Email notifications for CSV exports for the following supported languages pt_BR, zh_CN, zh_TW fall back to English.

To Reproduce

1. Browse to WP Admin -> Users -> Profile
2. Change the profile language to any of the languages above.
3. Run a CSV export of transactions, payouts or disputes, making sure you have more than a single pagination to trigger a server export
4. Check the language of the email triggered, and the CSV contents. It should be in user language but is provided in US English.

Detailed observations here #10003 (review)

Additional context

• The server uses dash-separated locales e.g. pt-br, zh-cn, zh-TW
• WordPress core at the client side, uses locale in the format pt_BR, zh_CN etc.
• We have a utility function convert_to_server_locale() that roughly converts the WordPress core locale type to the server supported dash-separated locales.
• The CSV export POST request params incorrectly include the locale en_US. This is likely a bug that occurs when the request query params are prepared in convert_to_server_locale().
• The issue was found while creating the PR - CSV Exports: Simplify localization by setting export language to that in user profile settings #10003