After the midnight service, people walk through the streets carrying torches, playing guitars and beating on tambourines and drums. One Spanish saying is 'Esta noche es Noche-Buena, Y no Es noche de dormir' which means 'Tonight is the good night and it is not meant for sleeping!'
A few different languages are spoken in different regions in Spain. In Spanish Happy/Merry Christmas is 'Feliz Navidad'; in Catalan it's 'Bon Nadal'; in Galician 'Bo Nadal'; and in Basque (or Euskara in basque) 'Eguberri on'. Happy/Merry Christmas in lots more languages.