apply_filters( 'wp_mail_charset', string $charset )

More Information

• The default character encoding for wp_mail() is UTF-8. The character encoding can be changed using the wp_mail_charset filter.
• While the average user is unlikely to need to change the default character encoding for email, users who need to send email in different languages may find this filter useful.
• UTF-8 is still the recommended default character encoding to use since it’s backward compatible with ASCII and can represent nearly all languages. As a result, UTF-8 is the most ubiquitous character encoding being used on the web. Users/developers typically do not need to change the character encoding in order to read/write foreign langauges.
• As of Version 3.5, WordPress character encoding is no longer configurable from the Administration Panel and defaults to UTF-8.