If a resource has multiple language variants and the difference between variants is only in the language of human-readable fields, then the Accept-Language request HTTP header SHOULD be used to select the desired language variant.
GET /article HTTP/1.1
Accept-Language: en,en-US,fr;q=0.6
HTTP/1.1 200 OK
Content-Type: application/hal+json;charset=UTF-8
Content-Language: en
Vary: Accept-Language
...
If the difference between language or country specific variants of a resource is bigger than just in the content of human readable strings, for example, the data structure of the resource representation is different, then a query parameter SHOULD be used to communicate the requested variant.
GET /article?market=en_US HTTP/1.1
HTTP/1.1 200 OK
Content-Type: application/hal+json;charset=UTF-8
Content-Language: en
Vary: Accept-Language
...