Redirection to sub sites in multi site after login

hi i have a simple question, on a multi-site (directory)
When a user login to a sub site, he goes directly to the dashboard , how can i redirect him to the sub-site (siteurl)
ex with http://www.mysite.com/fr
now the user goes after login to http://www.mysite.com/fr/wp-admin i just want him to go to http://www.mysite.com/fr
thx for your answers