You can use the keywords deaf* AND specific country or search using "sign language" AND (world OR international OR global) or "sign language" AND specific country to retrieve results. You can also use the keywords (deaf* OR "sign language") AND the country's name if you are interested in a specific country.
The asterisk * next to the keywords will find variations in the spelling of that word, i.e., Deafened, Deaf-Blind, etc.