Non-ASCII characters in email messages are transformed to ???? when the platform encoding is not UTF-8

Steps to reproduce:

1. Run Crowd in a platform where the default character encoding is not UTF-8.
2. Set the password reset email template to a text containing non-ASCII characters.
3. Send a password reset email for some user.

Expected result: an email containing correctly-encoded UTF-8 characters.

Actual result: non-ASCII characters appear as question mark characters .