One ArcaOS 5.1 license (new or upgrade) will entitle the customer to download the language of his choice. He may, in fact, subsequently download a different language. All available languages will be selectable from his download portal.
ArcaOS 5.1 is available in either personal and commercial editions. Personal edition licenses come with a 6 months ArcaOS Support & Maintenance subscription. Commercial editions include prioritized support and a full year ArcaOS Support & Maintenance subscription.
See ArcaOS FAQ for additional details.