I used to live in New Mexico. I'm aware of the fights for many years to get statehood for New Mexico, and I'm aware of the issues in Congress in the late 1800s and early 1900s with people who tried to keep New Mexico out of the Union on the grounds that it was not sufficiently American. The New Mexico territory was finally divided in half and admitted as two separate states.
Precedents count. I cannot see any good reason that mandatory English-only requirements should be imposed on Puerto Rico as a condition of statehood when that has never been done before with a state. Also, given population shifts, Puerto Rico does not pose a demographic or cultural threat to the United States; we've got serious concerns with assimilation of Mexican immigrants along our southwest border, but Puerto Rico is not exactly a center of population growth.
BTW, before Michigan was a state, for quite some time after not only the American Revolution but also the War of 1812, the English-speaking residents were considered likely British sympathizers and it was the French-speaking people who the American government considered trustworthy. Granted, by the time Michigan was admitted to statehood, French-speaking fur traders and trappers were receding into irrelevance as English-speaking farmers were beginning to fill up the southern counties.
Thank you for your insight.