parameter completely ignored

[jmandel]

Bug

The displayLanguage parameter has no effect on $lookup responses. The display is always in English regardless of the requested language. Even a nonexistent language tag like xx produces no error.

This contrasts with $validate-code, where displayLanguage works correctly.

Repro

# Request German display — returns English
curl -s 'https://tx-dev.fhir.org/r4/CodeSystem/$lookup?system=http://loinc.org&code=8480-6&displayLanguage=de' \
  -H 'Accept: application/fhir+json' | jq '.parameter[] | select(.name=="display") | .valueString'
# Returns: "Systolic blood pressure"
# Expected: "Systolischer Blutdruck" (or similar German translation)

# $validate-code DOES honor displayLanguage (for comparison):
curl -s 'https://tx-dev.fhir.org/r4/CodeSystem/$validate-code?url=http://loinc.org&code=8480-6&displayLanguage=de' \
  -H 'Accept: application/fhir+json' | jq '.parameter[] | select(.name=="display") | .valueString'
# Returns: "Systolischer Blutdruck" (correct)

Reproduces on both servers.

Spec reference

R4 section 6.4.18: displayLanguage (IN, 0..1, code) for $lookup — "The requested language for display."