What does oh chante mean in French?

"oh chante" is an invitation to someone to sing. "oh" is just a marker, like you would find in poetry when addressing the sun or a marvellous creature. "chante" is a form of the verb "chanter", to sing.

the writing of "chante" indicate that the verb is used in the imperative mood.

"oh rossignol chante, la fin de l'été

tu as le cœur à rire, je l'ai à pleurer..."

"oh Nightingale sing, the end of Summer,

you're in the mood to laugh, I'm in the mood to weep.."

('à la Claire fontaine', traditional French song.)