JSFiddle - React, Tailwind, and code Playground

JavaScript

function language(lang){
    var translations = {
        vn : {
            error_fname : "Tên",
        },
        en : {
            error_fname : 'First Name',
            error_lname : 'Last Name'
        }
    };
    
    var currentLang = 'en'; // default
    
    function get(key){
        return translations[currentLang][key];
    }
    
    // public pointers
    this.get = get;
    
    // constructor
    if(typeof lang != 'undefined' && translations[lang]){
        currentLang = lang;   
    }
}

var language = new language('en');
console.log( language.get('error_fname') );