Validation of 'http://ahangama.com/election/whatnext-s.htm'

That page is written in Romanized Singhala, and rendered in the native 
script using an Orthographic Smartfont.

I feel the meta data, lang='si-Latn' conveys the correct information. 
However, I have not registered this notation. Please help me to do it 
properly. It would be much appreciated.

Thank you.