从.htaccess seo url中删除默认语言

I rewrite multi language Url using .htaccess like this :

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(fr/en)/(article|page|gallery)/([0-9]+)/([A-Za-z0-9-]+)/?.html$ index.php?page=$2&id=$3&title=$4&lang=$1 [NC,L,QSA]

Output Is :

http://localhost/subdomain/fr/article/1/title1.html
http://localhost/subdomain/en/article/2/title2.html

this worked true for two language (fr/en). my default language is en and I need to remove en from slug url like this :

 http://localhost/subdomain/article/2/title2.html

my mean is remove en from seo url only for language is default en. how do can I generate this ?!

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f

#Rule for "en"
RewriteRule ^(article|page|gallery)/([0-9]+)/([A-Za-z0-9-]+)/?.html$ index.php?page=$1&id=$2&title=$3&lang=en [NC,L,QSA]
#____________

#Rule for "fr"
RewriteRule ^(fr)/(article|page|gallery)/([0-9]+)/([A-Za-z0-9-]+)/?.html$ index.php?page=$2&id=$3&title=$4&lang=$1 [NC,L,QSA]