Rdf 如何从源数据生成语言标记

我正在使用并希望像这样映射模式

<title>
  <string language="en-US">Golf Explained</string>
  <string language="es">Explicó Golf</string>
</title>

这是可行的，但对英语来说不行。如何从/lom/general/title生成语言标记/string@language替换“en”

我试过了

  rr:predicateObjectMap [
  rr:predicate sdo:name;
  rr:objectMap [
    rml:reference "/lom/general/title/string";
    rr:termType rr:Literal;
    rr:language  [rml:reference "/lom/general/title/string/@language"]  
  ]
];

无久益“语言标签”node1ef4p39f8x5“不符合BCP 47标准”

  rr:predicateObjectMap [
  rr:predicate sdo:name;
  rr:objectMap [
    rml:reference "/lom/general/title/string";
    rr:termType rr:Literal;
    rr:language  "en"  
  ]
];

  rr:predicateObjectMap [
  rr:predicate sdo:name;
  rr:objectMap [
    rml:reference "/lom/general/title/string";
    rr:termType rr:Literal;
    rr:language  [rml:reference "/lom/general/title/string/@language"]  
  ]
];