Clean URL, read more at https://ahonerd.com/htaccess

.htaccess

RewriteRule ^en$ /?&%{QUERY_STRING}
RewriteRule ^jp$ /?&%{QUERY_STRING}
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_URI} /(.*)/$
RewriteRule ^ /%1 [R=301,L]

RewriteRule ^en/([a-zA-Z0-9-]+)/([a-zA-Z0-9-]+)$ /index.php?page=$1&sub=$2 [L,NC,QSA]
RewriteRule ^en/([a-zA-Z0-9-]+)$ /index.php?page=$1 [L,NC,QSA]
RewriteRule ^jp/([a-zA-Z0-9-]+)/([a-zA-Z0-9-]+)$ /index.php?page=$1&sub=$2 [L,NC,QSA]
RewriteRule ^jp/([a-zA-Z0-9-]+)$ /index.php?page=$1 [L,NC,QSA]
RewriteRule ^([a-zA-Z0-9-]+)/([a-zA-Z0-9-]+)$ /index.php?page=$1&sub=$2 [L,NC,QSA]
RewriteRule ^([a-zA-Z0-9-]+)$ /index.php?page=$1 [L,NC,QSA]