I think what the President means is, when The Star-Spangled Banner is sung, it should be sung in English.
When The Star-Spangled Banner is signed, it is signed in the form most commonly used in the United States. It is not signed in Mexican Sign Language, French Sign Language, Italian Sign Language, etc.
The national anthem of any country should be sung in the official or most commonly used language of that nation.
National anthems are used to unify people as one people and one country. If each group within the country sings the "national" anthem any way they want, in any language they want, then the unifying factor is lost. Can you imagine a gathering of people at a public event all singing the National Anthem in different languages at the same time? Aack!
The Spanish version of The Star-Spangled Banner doesn't even use the same title, and the "translation" isn't even close to the original text.