Quite simple. Many well-known phrases have a country’s name or nationality in them… eg German measles,Danish pastry,Maltese cross. Some may use the country name…Canada Dry,Ulster fry.
The challenge is how many different countries you can find a well-known phrase for…(please keep it something we’ll have heard of)
You can go for variations eg Siamese/Thai.
Can we go round the whole world?You’ve had five starters to help you out…brains begin now 
French toast? 
And you didn’t go for French kiss or French knickers…truly an angel
Oh man, all the ones I know are variations of the “English Method.”
Dutch Courage
American dream
White Russian
Mexican Standoff
Canadian Bacon
Russian roulette
Chinese Fire Drill
Welsh rarebit
Australian crawl
Indian summer
Spanish Fly…
Swedish meatballs
India ink
Irish temper
-French letter
-French cap
-French fry
-German chocolate cake
-Dutch uncle
-Panama hat
-Scotch eggs
-Black Russian
-Afghan[the knitted/crocheted cover]
-Irish coffee
-Italian salute
Dutch Oven
Dutch Apple Pie
Belgium Waffle
German Chocolate
Brazil nut
Canadian Club
Chinese Checkers
Does ‘Baked Alaska’ count?
French Vanilla
Egyptian Cotton
Double Dutch
Mexican turnover (As a magician, this is used quite a bit)
Canadian goose
Spanish Stairs (Located in Venice, Italy)
Spanish Steel
Venitian Blinds
Spanish Rice
Black Russian (Alcoholic drink)
French tickler
Siamese twins
Jamaican jerk chicken
Panama Jack
bamf