Actually, I think I'm wrong...
If you have multiple language versions of a URL, each language page in the set must use rel="alternate" hreflang="x" to identify all language versions including itself. For example, if your site provides content in French, English, and Spanish, the Spanish version must include a rel="alternate" hreflang="x" link for itself in addition to links to the French and English versions. Similarly the English and French versions must each include the same references to the French, English, and Spanish versions