[SalesForce] Conditional formatting in HTML Email Templates

I tried to complete your code to achieve what you describe and found a little problem: sending the email will create a Task object, which conflicts with saving an EmailTemplate (you get a MIXED_DML_OPERATION).

What I ended up doing is creating separate buttons for the save and the email. I used a TemporalTemplate to store the modified version so I can reuse it.

You may be able to avoid the MIXED_DML_OPERATION by using a @Future method to send the email after the save.

Here's my code:

<apex:page controller="EmailTemplateController">
<apex:form >
<apex:pageBlock >
<apex:pageBlockButtons >
<apex:commandButton action="{!sendMail}" value="Send Email"/>
<apex:commandButton action="{!saveTemplate}" value="Save Template"/>
</apex:pageBlockButtons>
<apex:pageBlockSection columns="1">
<apex:pageBlockSectionItem >
    <apex:outputLabel value="Target Contact" />
    <apex:inputField value="{!targetContact.ReportsToId}"/>    
</apex:pageBlockSectionItem>
<apex:pageBlockSectionItem >
    <apex:outputLabel value="Edit Template" />
    <apex:inputTextarea id="editTemplate" value="{!editedTemplate}" richText="true" cols="100" rows="15"/>
</apex:pageBlockSectionItem>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>

And the controller:

public with sharing class EmailTemplateController {
    public Contact targetContact {get;set;}
    public String editedTemplate {get;set;}
    private String templateId = null;
    public EmailTemplateController() {
        targetContact = new Contact();
        if (ApexPages.currentPage().getParameters().containsKey('template')) {
            templateId = ApexPages.currentPage().getParameters().get('template');
            this.editedTemplate = [select HtmlValue from EmailTemplate where Id = :templateId].HtmlValue;
        }
    }

    public PageReference saveTemplate() {
        EmailTemplate template =  [select Id, HtmlValue from EmailTemplate where Name = 'TemporalTemplate'];
        template.HtmlValue = editedTemplate;
        update template;

        return null;
    }

    public PageReference sendMail() {
        EmailTemplate template =  [select Id, HtmlValue from EmailTemplate where Name = 'TemporalTemplate'];

        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
        email.setSenderDisplayName('Tester');
        email.setTemplateId(template.Id);
        email.setTargetObjectId(targetContact.ReportsToId);
        Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});
        return null;
    }
}

Are you adding them via .csv? If the encoding of the file that is storing the information is Unicode (or whatever encoding is needed) the Data Extension should accept it correctly since you said they are set to a field type of 'text.'