.htaccess for multilanguage website - .htaccess

Question

So I want to build a multilingual website.
At first I thought about setting language parameters through cookies, but Google says that it is not recomended. And I don't want to mess with Google because most of my visitors comes from search engines.
Google suggests subdomains likes lang.example.com or directories like example.com/lang
But I don't want to create multiple subdomains and directories in my host, so I will just use lang parameter in the URL like example.com/home?lang=de or example.com/about?lang=fr
And of course I want it to look like directories. I tried multiple htaccess configurations, but it either doesn't work at all or messes up my other rewrite rules with multiple parameters.
My old working htaccess looks like this:
RewriteRule ^about/?$ ?page=about [NC,QSA]
RewriteRule ^home/?$ ?page=home [NC,QSA]
RewriteRule ^browse/?$ ?page=browse [NC,QSA]
RewriteRule ^contact/?$ ?page=about&what=contact [NC,QSA]
RewriteRule ^message/?$ ?page=about&what=send [NC,QSA]
RewriteRule ^browse/([^/]+)$ ?page=make&make=$1 [NC,L,QSA]
RewriteRule ^browse/(.+)/(.+)/?$ ?page=browser&make=$1&ser=$2 [NC,L,QSA]
I tried adding
RewriteRule ^de/(.*)$ /$1?lang=de_DE [L,QSA]
and similar configurations, but it never works how I want.
Any ideas how to make it work?

Answer 1

Have your rules like this:
RewriteEngine On
# handle URIs with language parameters like /en/, /it/, /de/, /fi/ etc
RewriteRule ^([a-z]{2})/(about|home|browse)/?$ ?page=$2&lang=$1 [NC,QSA,L]
RewriteRule ^([a-z]{2})/contact/?$ ?page=about&what=contact&lang=$1 [L,NC,QSA]
RewriteRule ^([a-z]{2})/message/?$ ?page=about&what=send&lang=$1 [L,NC,QSA]
RewriteRule ^([a-z]{2})/browse/([^/]+)/?$ ?page=make&make=$2&lang=$1 [NC,L,QSA]
RewriteRule ^([a-z]{2})/browse/([^/]+)/([^/]+)/?$ ?page=browser&make=$2&ser=$3&lang=$1 [NC,L,QSA]
# defaulting to english
RewriteRule ^(about|home|browse)/?$ ?page=$1&lang=en [NC,QSA,L]
RewriteRule ^contact/?$ ?page=about&what=contact&lang=en [L,NC,QSA]
RewriteRule ^message/?$ ?page=about&what=send&lang=en [L,NC,QSA]
RewriteRule ^browse/([^/]+)/?$ ?page=make&make=$1&lang=en [NC,L,QSA]
RewriteRule ^browse/([^/]+)/([^/]+)/?$ ?page=browser&make=$1&ser=$2&lang=en [NC,L,QSA]