You can use a single Campaign with Conditions for each country. In the Condition you would use the "Field is this value" condition and select the Country field. If it is equal to the United States then have the English language email sent on the "Yes" path. On the "No" path add a condition for the second country ("Mexico") in my example here:
Depending on how often you do this you can employ other automation steps. If you are sending a monthly newsletter you can have this campaign, and just edit the Email elements for each month.