English vrs other languages

U.S. refuses to participate in International Mother Language Day until it's celebrated only in English

This article came to my attention when I read "U.S. refuses to participate in International Mother Language Day" Why, once again, will the U.S. refuse to participate in an international day designated by the UNESCO? The answer was just because is not in English.
I understand that many immigrants (being one myself) bring their own language to this country and try to impose it over English. I do not agree to this and I am all pro making English the nation's official language, but why not celebrate the different languages and cultures that make this country.

We should not forget that the United States was founded by immigrants. We all together natives and foreigners make up this country. Many even if is not the majority speaks a mother language other than English and is really important to them. Is not fair that they are not given the opportunity to celebrate their own modern tongues along with English which they also use.