Pronunciation of vowels will often reveal if they learned their English on the European continent or North America, or even the Antipodes. Pronunciation of certain consonant constructions will place them as to approximately where on the European continent they come from.
Certain words such as boot for trunk, lift for elevator, queue for line, lorry for truck, loo for toilet, will do that as well—if they use the first word in each example will tell you that they more than likely learned their English on the continent. As stated above, multisyllable words will give them away as to which syllable they emphasize.
People with mother tongues in Germanic languages often have a problem with prepositions and prepositional phrase placement in sentences.
People from some Slavic languages, such as Czechs will have problems with gender, especially giving gender to inanimate objects. Some Poles and Polynesians have problems with tense. All Slavics and Germanics will sometimes have problems pronouncing “V“as “W” and “W” as “V” in English.
Haitians cannot properly pronounce the herb perejil, or parsley in Spanish. When Dominican Republic closed it’s border to Haitian migrant workers in DR—many Haitians could mimic DR Spanish perfectly except for that one word—and border guards would simply ask any suspected Haitians to pronounce perejil properly and when they couldn’t they were shot in situ. It was known as the Parsley Massacre, or Parsely War.
Scandinavians often make the mistake of mispronouncing the English word “Union” when casually reading it as “Onion”. LOL.
Spaniards can place certain Latin Americans by the way they pronounce their S’s. Spaniards, Cubans and a few New Worlders pronouernce it properly with a lisp, as in Cathtille, instead of Castille. Others, like Mexicans pronounce the S like an S. Same with the double “L” construction. Some pronounce Caballo as Cabayo, and still others pronounce it as Cabajho, with a soft “j” sound. Then there is the name ””, pronounced variously with an almost gutteral sound in the back of the throat for the J, in other places they pronounce it Zhwahn, and still others as Whan. Spanish-speaking people are very good at identifying where other Spanish-speaking people come from.
These things slip out in even the best linguists when they are fatigued or have been drinking.