Вы также можете использовать I18n:
I18n.t("date.month_names") # [nil, "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"]
I18n.t("date.abbr_month_names") # [nil, "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
I18n.t("date.month_names")[Date.today.month] # "December"
I18n.t("date.abbr_month_names")[Date.today.month] # "Dec"