Hi Michal,
Thank you for the soon and detailed reply !
I have understood your point very well !
so, now If you tell me that ( the &lang have no big influence on to functionality of anything and you can use JoomSEF and JoomFish together without any problems)
My website is really blocked if i enable seo on my joomla configuration !
When i activate seo and navigate on my website, all links seems well sef only the language selector for english . And if i click on it no page content can displayed i have simply a white page on the body.
For that i can't enable seo on my global setting, if you accept to take a look, please let me know and i will activate it for you to see the bug !
So thank you very much for all your effort.