Using multiple languages in email template is possible using the Visual force email templates.

Visualforce email templates translation is based on, for example, the recipient user's language or the language specified for an account. To translate Visual force email templates based on recipients' or related objects' languages, use the

<messaging:emailTemplate> tag's language attribute (valid values: Salesforce.com supported language keys, for example, “en-US”). The language attribute accepts merge fields from the email template's recipientType and relatedToType attributes. You create custom language fields for use in the merge fields. The translation workbench is needed to translate email templates.

This example uses a merge field to obtain a language attribute for the contact receiving the email:
 

<messagingmessaging:emailTemplate subject="Welcome!" recipientType="Contact"
relatedToType="Account" language="{!recipient.language__c}">
<messaging:plainTextEmailBody>
{!$Label.greeting}
</messaging:plainTextEmailBody>
</messaging:emailTemplate>

Please find below the documentation for the VF email templates

>> Creating a Visual force Email Template:
http://www.salesforce.com/us/developer/docs/pages/Content/pages_email_templates_creating.htm?SearchType=Stem&Highlight=translating|translate|Translation|translations|Translated|translation

Unfortunately, at present no other functionality inside Salesforce can be used to achieve this.

There are existing ideas in Idea Exchange for this functionality within Salesforce. You can also promote this Idea so that It can be merged in future releases.

>>Email Templates in Multiple Languages:
https://success.salesforce.com/ideaView?id=08730000000BqWPAA0

>>Include Google Translate feature for emails
https://success.salesforce.com/ideaView?id=087300000007uDHAAY

>>Automatic text translation link
https://success.salesforce.com/ideaView?id=08730000000BqYYAA0