URL Rewrite for multilingual Website

Question

Hello, I have a problem:

I have an URL like that :

/eng/myfolder/mycategory.aspx

I would like to transform it in something like:

index.aspx?FolderId=2&LanguageId=1&CategoryID=12

In a word I want to "write" that,

eng =>  languageId=2  and myfolder => FolderId=2 and mycategory.....

I don't know if i make myself clear but

I was thinking to make a dynamic "rules with rewrite map" but i don't know how do that

Maybe with http://mywebsite.com/default/fr

Something like:

 <add key = "/en"  value = "/LanguageId=1" />
 <add input = " {Rewrite:{REQUEST_URI}}" pattern = "default/(.+)" />
 <action type="rewrite" url="default.aspx?{C:1}" appendQueryString="False" />