Before the Horcrux in his body got destroyed, Harry could speak to snakes, right?
However, the whole ''conversation'' sounded just like English to him, right? That's fine.
But But if Harry were a bilingual child, which language would the conversation with a snake sound like to him?
If he spoke both French (or any other language, for instance) and English fluently, what would he understand from a snake?
You could argue that the conversation would sound like English, because it is his native language, but what if he were born in a bilingual country?