1. Create a custom field in JIRA.
2. Translate custom field into another language (language B)
3. Change JIRA language to language B
4. Ensure Confluence is in language A.
5. Insert JIRA issues macro and adjust display options to ensure it will include custom field.
6. Custom field will display in language B, the other fields in language A, matching Confluence's profile language.
7. Change JIRA back to language A.
8. Check Confluence, custom field is still in language B.
9. Edit page, re-insert JIRA issues macro, and language will now be in language A.
10. Change Confluence to language B, custom field is still in language A

Tested in English/Japanese, and it's reported also in English/German