Not sure. Previously you could edit the file "Local State" (found in your profile) to tell it you were located in the US but I've since had reports of that not working. Still, if you want to try it ...

Go to About Opera from the menu, and copy the path listed for Profile. Close Opera, open a file manager window (such as My Computer) and paste the path to your profile in the location bar. Open the file Local State in a text editor such as Notepad or Wordpad. Find the section "location"; on my system it looks like this:

"location":{"country":"us","country_from_server":"US","timestamp":"1419298826600000000"},

Change you country and country_from_server as you see above, and make sure the timestamp is somewhere reasonable (probably can just leave it as you found it), then save the changes. Next time you start Opera it should use google.com ...