Options +FollowSymLinks
RewriteEngine On

#categories
RewriteRule ^([1-9][0-9]?)cat([0-9][0-9]*)\.html(&.*)? index.php?lang=$1&idcat=$2$3
RewriteRule ^cat([0-9][0-9]*)\.html(&.*)? index.php?idcat=$1$2

#pages
RewriteRule ^([1-9][0-9]?)side([1-9][0-9]*)\.html(&.*)? index.php?lang=$1&idcatside=$2$3
RewriteRule ^side([1-9][0-9]*)\.html(&.*)? index.php?idcatside=$1$2