Russian has two words for ‘you’, the informal ты and the formal вы. Various strategies are used in translation to convey the difference, but in this poem, which relies on the contrast between the two, I think the best way is the now archaic thou vs. you distinction. To do otherwise and just use ‘you’ for both would be unfaithful to the original, which relies on the social implications of mixing up the two pronouns. It was obviously a big enough blunder for the besotted Pushkin to write a poem about it. More importantly, ignoring the thou/you divide would rob the poem, in particular, its last line, of its impact.
Thou and you
The empty you with hearty thou
She mixed up carelessly in error
And all the joys I can’t allow
She set alight in me, like terror.
I stand in thought, my mind runs free,
I’m staring, and she’ll think I’m smarming;
I tell her, “you are very charming”
But thinking: “how I do love thee!”
Пустое вы сердечным ты
Она, обмолвясь, заменила
И все счастливые мечты
В душе влюбленной возбудила.
Пред ней задумчиво стою,
Свести очей с нее нет силы;
И говорю ей: как вы милы!
И мыслю: как тебя люблю!
Alexander Pushkin, 1828