In order for EE Classifieds to send email notifications in Chinese, I translated the original mail.sql (English) by hand. I changed the locale-field value from ‘en_US’ to ‘zh_TW’. It is also important to put the translations in UTF-8 encoding.
Despite mail.sql being included in each language-pack, the file is not always executed. That means translated email templates are not always loaded into database when the language pack is installed/updated.
One reason is that the mail.sql uses ‘INSERT INTO’ statements. Executing mail.sql fails if email-template of the same language is already in the database.
[Resolution] I modified the mail.sql to issue SQL command REPLACE INTO instead of INSERT INTO for each template instance.
Another reason is that the SQL-script was not executed at all.
[Resolution] It is possible to update the Email-Templates without re-installing the language package: upload the translated email-template at the ‘Import Data’ function of OSClass Admin Interface.
Settings > Tools > Import Data