If you're sending emails that contain a foreign language, it's likely that you're using special characters that may not render correctly in the email inbox.
May render in the inbox as:
1. Convert all special characters to HTML entities. You can use an HTML Character Converter such as provided by Email on Acid.
Should be converted to:
2. Alternatively you can add the following code to the first line of your HTML document:
<?xml encoding="utf-8" ?>