var normaliseLang; normaliseLang = function (lang) { lang = lang.replace(/_/, "-").toLowerCase(); if (lang.length > 3) { lang = lang.substring(0, 3) + lang.substring(3).toUpperCase(); } return lang; }; $.defaultLanguage = normaliseLang( navigator.languages && navigator.languages.length > 0 ? navigator.languages[0] : navigator.language || navigator.userLanguage ); var lang = normaliseLang( $.defaultLanguage); fetch('data/spells/spells-grimoire-fr.json') .then((response) => response.json()) .then((json) => JSON.parse(json)); var string jsonsource = ''.concat("../data/spells/spells-grimoire-",navigator.languages[0].slice(0,2),".json"); import data from jsonsource assert { type: 'json' }; console.log(data); var yourHtml = JSON; document.getElementById("spell-list").innerHTML = yourHtml;