function add(el, lang, sel) {
                var elo = {
                    "element": el,
                    "selector": sel
                };
                if (!list.has(lang)) {
                    list.set(lang, []);
                }
                list.get(lang).push(elo);
                counter[0] += 1;
                return elo;
            }
Add element to elements
@param {object} el The element
@param {string} lang The language of the element
@param {string} sel The selector of the element
@returns {Object} An element-object