Charles li reis, nostre emperesdre magnes,
Set anz totz pleinz ad ested in Espagnes.
A translation would be most helpful. It looks like a mixture
of Spanish and Mediaevel French...ah, it is the La Chanson de
Roland.
Yes, it's Old French, and means "Charles the king, our great emperor[*] / Seven full years has been in Spain." You pronounce it pretty much like Spanish, except for the "z" which is pronounced "ts".
[*] Old French had two noun cases, nominative and oblique (a combination of the Latin genitive, dative, accusative, and ablative). In 99% of modern French nouns, only the oblique survives. In particular, "emperesdre" is the old nominative of "empereor"; it survives today in the name "L[']empriere".
A dozen nouns picked up different semantics in the nominative and both survived: sire/seigneur, prêtre/Provoire (proper name), copain/compagnon, pâtre/pasteur, chantre/chanteur , maire/majeur, gars/garçon, and (most surprising) on/homme. In a few nouns, only the nominative survives: soeur, peintre, traître (English traitor is from the oblique), and the names Charles, Georges, James (now in English only), Hugues, Marie, and Eve.