Add "?lang=en" to the end of my links

Hi,

I’m looking to add “?lang=en” to the end of my links like so… http://example.com/?lang=en, http://example.com/pageone?lang=en

I have been messing around with the .htaccess file and failing with my results. Can anyone point me in the right direction to achieving this. Any help with this would be greatly appreciated.

Thanks in advance.