We don't have any news to share when the Google Home app is available in Sri Lanka. Also, since Google Nest devices aren't officially supported in your country, it may or may not work. You can try changing your phone and Google Assistant language and region to any supported countries but again it's not guaranteed to work.
We're always looking for ways to improve and to bring more devices to different regions. Let me know if I can assist with anything else, otherwise I’ll be locking this thread after 24 hours.