Welcome to America.......now speak English!!!!
As much as you may want to, you're not going to stop an influx of foreign language influence. Even legal immigrants are going to bring their language. We barely speak "English" ourselves. Go find someone from England. Listen to their dialect (or as a British coworker of mine used to say - "proper English"
). Then listen to our language. Mutually intelligible, sure, but very, very different in phraseology. Much of that is due to us being separated and subject to influences from many other languages brought over by immigrants. Just look at the situation in Louisiana where a good chunk of the population still speaks an oddball variant of French (as someone who actually can speak a little French, I can honestly say it's definitely "oddball" - it's "French"-ish, but incredibly hard to understand).
In regards to Spanish - like it or not, we share a border with a huge country with a Spanish-speaking population. You're going to get a lot of mixing of language there. We're going to get a lot of immigration - both legal and not - and those people, even if they do learn English, are not going to just forget or give up their native tongue for your benefit. Eventually I'd expect the two languages to merge into one over time. You can kinda see examples of that already. For example: cilantro. The actual English word for this herb is coriander, but everyone I know of - even those who only speak English - use the Spanish term for it - cilantro. Expect more borrowed words and blending over time. It's already happened in the past and constantly does. Compare our English with the English used in the KJV bible (late 1500's) and notice how differently it looks. Go a little further back and read the Canterbury Tales and notice how odd that looks. Or if you REALLY want a shock: go back and look at the Old English Beowulf. Just for comparison, here is the first paragraph of it:
HWÆT, WE GAR-DEna in geardagum,
þeodcyninga þrym gefrunon,
hu ða æþelingas ellen fremedon!
oft Scyld Scefing sceaþena þreatum,
monegum mægþum meodosetla ofteah,
egsode eorlas, syððanærest wearð
feasceaft funden; he þæs frofre gebad,
weox under wolcnum weorðmyndum þah,
oð þæt him æghwylc ymbsittendra
ofer hronrade hyran scolde,
gomban gyldan; þæt wæs god cyning!
Ðæm eafera wæs æfter cenned
geong in geardum, þone God sende
folce to frofre; fyrenðearfe ongeat,
þe hie ær drugon aldorlease
lange hwile; him þæs Liffrea,
wuldres Wealdend woroldare forgeaf,
Beowulf wæs breme --- blæd wide sprang---
Scyldes eafera Scedelandum in.
Swa sceal geong guma gode gewyrcean,
fromum feohgiftumon fæder bearme,
That's "English" circa the turn of the previous millennium. Languages evolve. The Spanish (and French, and Italian) that we hear today was once Latin. The English we speak actually descended from an older form of German (the original population of England spoke a form of Gaelic before being conquered by the Saxons). Until we reach a mutually intelligible blend though, many (on both sides) will have to deal with the limitations of being monolingual, or buckle-down and learn a second language. As a matter of fact, one of the primary factors by which a country's education system is judge is the percentage of people who speak more than one language - and America is sorely lacking in that metric.
