Android Stock Browser Not Override Accept-Language

Question

I have an Android Samsung tablet and I test this simple xhr request on its stock browser.

var url = "http://172.20.10.10:3030/whatever";
function reqListener () {
  console.log(this.responseText);
}

var oReq = new XMLHttpRequest();
oReq.onload = reqListener;
oReq.open("GET", url, true);
oReq.setRequestHeader("Accept-Language", "es-CL");
oReq.send();

Then, on my node server.

app.use(function(req, res, next) {
    console.log("HEADERS : ", req.headers['accept-language']);
    res.status(200).end();
    next();
});

I receive this header :

fr-FR,fr;q=0.8,en-US;q=0.6,en;q=0.4

Because my tablet is in french.

Is it possible to override this header on an Android Stock Browser ? To have :

es-CL,es;q=0.8,en-US;q=0.6,en;q=0.4

I reproduce too on Ucall, OnePlus...

Thank you !