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There are circumstances under which a person can become an American citizen without having to learn English, according to this source.

Literacy and Educational Requirements

Unless physically unable to do so, an applicant for naturalization must be able to speak and understand simple English as well as read and write it. However, if on the date of the examination the applicant is more than 50 years of age and has been a lawful permanent resident for 20 years or more, or the applicant is more than 55 years of age and has been a lawful permanent resident for 15 years or more, the applicant will be exempt from the English language requirement of the law. If exempt, the applicant may take the examination in any language.

All applicants physically able to write, must also be able to sign their names in the English language. However, the person mentioned above who is excused from knowing English is permitted to sign in a foreign language if unable to sign in English.

However, if on the date of the examination the applicant is more than 50 years of age and has been a lawful permanent resident for 20 years or more, or the applicant is more than 55 years of age and has been a lawful permanent resident for 15 years or more, the applicant will be exempt from the English language requirement of the law. If exempt, the applicant may take the examination in any language.

To my way of thinking, not learning our language after being a "lawful permanent resident" for 15 or 20 years should be reason enough to disqualify anyone from citizenship.