Hola,
Verifica en la ruta: /administrator/language/es-ES/es-ES.com_virtuemart.ini
Debe tener las lineas:
COM_VIRTUEMART_UNIT_NAME_100MG="100 miligramos" COM_VIRTUEMART_UNIT_NAME_100ML="100 mililitros" COM_VIRTUEMART_UNIT_NAME_CM="Centímetros" COM_VIRTUEMART_UNIT_NAME_CUBM="Metros cúbicos" COM_VIRTUEMART_UNIT_NAME_FOOT="Pie" COM_VIRTUEMART_UNIT_NAME_G="Gramo" COM_VIRTUEMART_UNIT_NAME_INCH="Pulgadas" COM_VIRTUEMART_UNIT_NAME_KG="Kilogramo" COM_VIRTUEMART_UNIT_NAME_L="Litro" COM_VIRTUEMART_UNIT_NAME_LB="Libras" COM_VIRTUEMART_UNIT_NAME_M="Metros" COM_VIRTUEMART_UNIT_NAME_MG="Miligramo" COM_VIRTUEMART_UNIT_NAME_MM="Mililitros" COM_VIRTUEMART_UNIT_NAME_ONCE="Onza" COM_VIRTUEMART_UNIT_NAME_SM="Metros cuadrados" COM_VIRTUEMART_UNIT_NAME_YARD="Yardas" COM_VIRTUEMART_UNIT_SYMBOL_100MG="100 mg." COM_VIRTUEMART_UNIT_SYMBOL_100ML="100 ml." COM_VIRTUEMART_UNIT_SYMBOL_CM="cm." COM_VIRTUEMART_UNIT_SYMBOL_CUBM="m³" COM_VIRTUEMART_UNIT_SYMBOL_FOOT="pies" COM_VIRTUEMART_UNIT_SYMBOL_G="g." COM_VIRTUEMART_UNIT_SYMBOL_INCH="pulg." COM_VIRTUEMART_UNIT_SYMBOL_KG="kg." COM_VIRTUEMART_UNIT_SYMBOL_L="l." COM_VIRTUEMART_UNIT_SYMBOL_LB="lb." COM_VIRTUEMART_UNIT_SYMBOL_M="m." COM_VIRTUEMART_UNIT_SYMBOL_MG="mg." COM_VIRTUEMART_UNIT_SYMBOL_MM="mm." COM_VIRTUEMART_UNIT_SYMBOL_OUNCE="onzas" COM_VIRTUEMART_UNIT_SYMBOL_SM="m²" COM_VIRTUEMART_UNIT_SYMBOL_YARD="yd."
Saludos.