English is my second-ish language, but perhaps I have an unfair advantage for this question since I spent nearly all of my childhood in the US and started learning English at age 5.

It wouldn't be outwardly noticeable, but the remaining non-native element for me would be the alphabet. I learned the English alphabet well before learning English itself, so the sounds of the individual letters are in my mind still part of my first language. In other words, whenever I recite the alphabet or spell words out loud letter-by-letter, it feels as though I am switching back to my first language.