A search showed that April Kim is based in Singapore and was the interpreter for Baemon and Taeyeon, and Lee Jieun used her at her Singapore and Malaysian concerts as well as her US concerts (apparently she used a local in her London concert) so it is likely that she bought April a business class ticket all the way to SG which is half a world away.
I think Lee Jieun will get more economical as she gains more foreign expertise
It is said Taylor Swift uses 50-200 staff, smaller for US concerts and larger for foreign concerts, and BTS uses 100-200 staff