Add new language

[itsnotsaved]

Is your feature request related to a problem?

Please add below language to disqus project https://www.transifex.com/disqus/public/

Language name: Sinhala Native name: සිංහල Code: si

Additional context

It was already requested years ago.

Available contributors: public statistic (transifex) @ruwank (requester) @HelaBasa (agency) @wa_chmd and maybe more