Such a notion is, in one way, preposterous. Our language is built out of foreign words. To know English is thus to know Latin, French, German, Dutch etc, and then there are all the additions, such as 'kosher', 'assassin', 'tsunami', which have been assimilated.
Elsewhere in that report it states just under half of older people are happy to try to speak the lingo when abroad, but those people were schooled in a different age, before the influence of belly-button gazing, child-centric methods completely took over.
When the teaching of facts is systematically stripped out of education, and replaced with the concept of self-expression, it's no wonder so many youngsters are incapable of conjugating a foreign verb, regular or irregular, or even recognising the French for 'hello'. Rousseau would most likely be very proud of these 'noble savages', notwithstanding the gulf of incomprehension which would separate him from them.