T4 (which stands for Text Template Transformation Toolkit) is a great way to automate code generation tasks. Here is a sample of how I translated resx file (which is kind of key/value xml) into JSON:

<#@ template debug="false" hostspecific="false" language="C#" #>  
<#@ assembly name="System.Core" #>  
<#@ assembly name="System.Xml" #>  
<#@ assembly name="System.Xml.Linq" #>  
<#@ import namespace="System.Linq" #>  
<#@ import namespace="System.Text" #>  
<#@ import namespace="System.Xml.Linq" #>  
<#@ import namespace="System" #>  
<#@ import namespace="System.Collections.Generic" #>  
<#@ output extension=".txt" #>  
{
<#  
XDocument resourceXML = XDocument.Load(@"C:\translations-en.resx");

var translations =  
        from tr in resourceXML.Descendants("data")
        select new Tuple<string,string>(tr.Attribute("name").Value, tr.Element("value").Value);                    

 foreach(Tuple<string,string> translation in translations)
 {#>
    "<#=translation.Item1#>" : "<#=translation.Item2#>",
<#}#>  
}