Bilingually ambidextrous, other than "incredible"? If this remark from an nyt article is correct, I'm awestruck at the mental agility required to pull it off:

Simultaneously , but does it also say spontaneously?
Or did he rehearse phrase by phrase. Just to imagine this trick
makes one's mind split.

Good grief, I couldn't do that in two languages that use the same alphabet!

No but you can use two syllables when the rest of the world uses only one Jackie!

The Pookwife's great grandfather could add up two columns of figures, one with each hand, simultaneously.

Technically I could write Greek and Latin simultaneously, but only one letter at a time by using those letters whose form (though not necessarily value) is common to both languages! Like A,B, E, P, etc.