Netherlands residents are the best non-native English speakers in the world, according to the EF English Proficiency Index. In the ten years that this index has been ranking English proficiency in various countries, the Netherlands has topped the ranking four times, and has never ranked lower than third.
The index based its figures on English test results of 2.2 million adults in 100 countries around the world. The participants had to complete various tests, including reading advanced texts, using "nuanced and appropriate" language in social settings, and negotiating a contract with a native English speaker.
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Netherlands has world's highest English proficiency for non-native speakers | NL Times