The people who feel threatened by non-English speakers are those Americans who speak no other languages. They probably took Spanish and French in HS and hated it, because learning a language involves a certain amount of drudgery when it comes to memorizing vocabulary, and of course, when one tries to speak a foreign language, it is embarrassing when people do not understand what they say or they do not understand simple questions such as the ones they are asked. Of course, Americans are really, really bad at teaching foreign languages. Language in general is a MAJOR trial for most Americans, since English is unphonetic in the extreme and hard to spell. Probably most Americans cannot write a coherent paragraph without making some sort of errors. Match is the other bugaboo. We know this because of all the complaints about how insufferably HARD it is to do the income tax. I admit I do not enjoy doing my taxes, but the hardest part is just getting the records together and remembering all the stuff I need to include. The math is a whiz, since I use an online program and actually do not have to do much math.
Most Americans have a sort of inferiority complex about all the stuff the do not know, such as language, history and geography, and they cover this up with a huge WE'RE NUMBA ONE giant rubber finger-waving superiority complex known as American Exceptionalism. Americans are certainly far from the bottom in our accomplishments, but we are NOT best at everything. We talk about how our system of government is "best in the world", when the reality is that is does not work much of the time, especially at the present moment, and there is not a single country that has adopted the more idiotic of our institutions, such as the Electoral College or the arrangement whereby different states compete with one another by luring businesses to themselves by spending taxpayer money to build roads, infrastructure and even buying land and building structures on it to give to the industries along with tax breaks for way longer than they should. Other countries NEVER adopt electoral colleges, and rarely have this "sovereign state" crap that beggars one state after another in a race to the bottom.