English their primary language if they want to pursue U.S. statehood, a statement at odds with the U.S. Constitution
I'm a little confused here and by no means am I even close to an expert on the Constitution, but the fact that it doesn't say English has to be their primary language to become a state doesn't mean the US can't/shouldn't require it by simply not voting them a state until they do adopt English. I doubt the Constitution says anywhere that a state has to have elected leaders instead of a monarch, but I'm sure that Congress would make that a requirement before even having a vote on it.
States don't have states rights until they are a state, do they? We can debate whether a requirement for them to adopt English is right or wrong, but I don't see how it's at odds with the Constitution.
Article IV - The States
New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State.
The Constitution is pretty open ended when it comes to making new states and Congress is the one who decides what requirements a territory needs.