Adjusting flatpickr Language based on User Language

Hello all, I'm currently using flatpickr in my survey. My survey is in both English and Chinese and I want my flatpickr to adapt to the language. I'm using following code but it seems that my if-else part is not working properly, so the flatpickr is displaying Chinese for the survey in both languages. I'm not very familiar with JS so would really appreciate any pointers. TIA!
I've put the following code in "Look and Feel" -> "General" -> "Header"




and the following code for the JavaScript part of my text entry question
if ("${e://Field/Q_Language}" == "EN"){
lang = "default";
} else {
lang = "zh";
}

Qualtrics.SurveyEngine.addOnload(function()
{
/*Place your JavaScript here to run when the page loads*/

});

Qualtrics.SurveyEngine.addOnReady(function()
{
jQuery("#"+this.questionId+" .InputText").flatpickr({
"locale": lang,
dateFormat: "Y-m-d",
minDate: new Date().fp_incr(-30),
maxDate: "today"
  });

});

Qualtrics.SurveyEngine.addOnUnload(function()
{
/*Place your JavaScript here to run when the page is unloaded*/

});