Question: The site has 2 languages: English and French, represented by 2 store views. French is the default one. For our SEO efforts we need to have the following urls:

1. French - <http://www.domain.com/category/product>
2. English - <http://www.domain.com/en/category/product>

System -> Configuration -> Web -> Add Store Codes to URL is the all or nothing setting. We just need to turn it off for the default store only.
I’ve done a lot of searching through the forums and wiki but there’s nothing on the subject. 

Please any sugestions?

Answer: 
Finnaly i solved this magic probleme , i hope that's save others persone here is the details : 

1- Download the zip existe in this page : <https://github.com/Knectar/Magento-Store-Codes>

2- unzip the file and put the folder called "Knectar" in {app/code/community/} and Knectar\_Storecodes.xml file in {app/etc/modules}

3- In your backoffice go to "System > Tools > Compilation" and click the rebuild button 

4- always in backoffice got to "System > Configuration > Web > URL options" and set the attribute "and default store view" to No and save the configuration

5- Clear your cach magento and enjoy your application :) .
I didn't find a quick solution to your problem, but I see that's possible through 2 steps : 

1 / Using the advise commented by @user3154108 and trying this tip <https://magento.stackexchange.com/questions/8126/store-code-in-url-for-every-store-view-except-for-default>
2 / For SEO SITEMAP, it's possible to override the following file 

```
app/code/core/Mage/Sitemap/Model/Sitemap.php
public function generateXml()
{
    ...
}

```

and replace the default store code by NULL.
For more details try to look at this post : <http://alanstorm.com/generating_google_sitemaps_in_magento>