Generally, you change your computer’s region from System Settings: Language and Region: Region.
If you want to overwrite this manually, follow the below steps (intermediate difficulty):
Quit Opera From the Terminal application, paste this line followed by Enter: open -e ~/Library/Application\ Support/com.operasoftware.Opera/Local\ State Look for and manipulate this line, "location": { "country": "us", "country_from_server": "US" } Save, and reopen Opera