The Verdict: Clear Path
You probably never lost French nationality, so there is nothing to reacquire. Renew your French passport, or ask for a certificat de nationalité française if you have no French papers.
Since 11 January 1973, a French adult who takes another citizenship stays French unless they formally declare that they give it up. An oath of allegiance elsewhere, or the other country telling you to renounce, does not end French nationality under French law.
If you still hold a French passport or identity card, even an expired one, the consulate can usually renew it. Otherwise you need the certificate. From abroad you apply to the Pôle de la nationalité française at the Tribunal judiciaire de Paris, on form Cerfa 16237*02, by post or in person, with no fee. The court has six months to answer and can extend that twice.
Check one thing first: whether you ever signed a formal French declaration of loss, usually at a consulate around the time you naturalised. If you did, the declaration route for former French citizens is the one to look at.
If you have lived abroad for a very long time without French papers, act soon. A separate rule stops people proving French nationality where the family has been abroad for 50 years without French documents.