Example

class WeekDays {
  static daysEs = ['Lunes', 'Martes', 'Miércoles', 'Jueves', 'Viernes', 'Sábado', 'Domingo'];
  static daysEn = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'];

  constructor (lang) {
    this.lang = lang;
    if(WeekDays.instance){
      return WeekDays.instance;
    }

    WeekDays.instance = this;
  }

  getDays(){
    return this.lang === 'es' ? this.daysEs : this.daysEn;
  }
}