index.js

const languages = ["en","fr"] 

const lists = [
  ["Underweight", "Normal Weight", "Overweight", "Obesity", "Obesity", "Obesity"],
  ["Insuffisance pondérale", "Corpulence Normale", "Surpoids", "Obésité modérée", "Obésité sévère", "Obésité mordbide ou massive"]
]

const chooseAdjs = lists[0]

module.exports = {
  bmi: (height,weight) => {
    if(isNaN(height) || isNaN(weight)) return console.error("ERR ! \n The height or weight isn't a number")

    const bmi = Math.round(weight / (height * height) * 10) / 10
    let str;

    if(bmi < 18.5) str = chooseAdjs[0];
    else if(18.5 <= bmi && bmi < 25) str = chooseAdjs[1];
    else if( 25 <= bmi && bmi < 30) str = chooseAdjs[2];
    else if( 35 <= bmi && bmi < 40) str = chooseAdjs[3];
    else if(40 <= bmi) str = chooseAdjs[4];

    return result = { bmi : bmi, adjective : str };
  },
  setLanguage: language => { if (languages.includes(language)) chooseAdjs = lists[languages.indexOf(language)] }
};