Currently there is no way in hydra to express a fixed number of possible values.

There seem to be no other established vocabularies which allow us to do so. At some point the RDF Shape WG shall provide a comprehensive way to express this and other constraints which then would supersede this proposal., But I think we need this earlier and I hope that hydra can provide valuable input to the Resource Shape WG by introducing such a facility which also integrates well with json-ld.

Proposal:
Have the following new properties and classes.

FIrst, hydra:allowedIndividual for enum values or other individuals with optional localized hydra:title to solve the value vs. caption problem.

* hydra:allowedIndividual :range hydra:AllowedIndividual - to hold the allowed individuals
  * hydra:AllowedIndividual - wrapper for allowed individuals with localized title
  * hydra:individual :domain hydra:AllowedIndividual - allowed URI values for a supported property

The :individual is for allowed values which are URIs, it should be used to apply @type:@vocab in the context.
Sample usage below. Client has requested Italian. The other language constructs of json-ld would work, too, see sample jsonld playgrounds below.

{
  "@context": {
      "@vocab": "http://schema.org/",
      "hydra": "http://www.w3.org/ns/hydra/core#",
      "hydra:individual": {
        "@type": "@vocab"
      }
  }
  ...
  "hydra:supportedProperty": [
      {
      "hydra:property": "eventStatus",
      "hydra:allowedIndividual": [
        {
          "hydra:individual": "EventCancelled",
          "hydra:title": "manifestazione annullata"
        },
        {
          "hydra:individual": "EventPostponed",
          "hydra:title": "manifestazione rinviata"
        } 
      ]
    }
  ]
}  

Second, hydra:allowedLiteral is for scalar values like strings or numbers.

* hydra:allowedLiteral - allowed literal values for a supported property

Finally, by dereferencing hydra:allowedResource the client can get a Collection or PagedCollection of allowed individuals which may have a search property in turn. This would be useful in case the number of allowed individuals is too large for :allowedIndividual.

* hydra:allowedResource - Resource or IriTemplate to retrieve allowedIndividuals

Also see http://tinyurl.com/qz85ep6 for a real-life JSON-LD playground example of allowedIndividual vs. allowedLiteral.
On http://tinyurl.com/om7fsqc one can see a language map.
On http://tinyurl.com/px4aj75 one can see an illustration for allowedResource with IriTemplate.