I don't know if this is the proper thread (I've just subscribed as recommended by Platonides, from WM-ES). I'm also working in the WLM organization and wanted to provide some information about the category handling in the monument lists in the Spanish Wikipedia. It covers all the Spanish territory (although the Catalan Wikipedia provides a more fine-grained listing for the monuments in Catalonia, the Valencia and the Balearic Islands).
{{Fila BIC
| nombre = '''[[Casa de las Alhajas]]'''
| nombrecoor = Casa de las Alhajas
| lugar = [[Plaza de San Martín (Madrid)|Plaza de San Martín]], 1<br />28023 [[Madrid]]
| lat = 40.418153 | lon = -3.706958
| fecha = {{fecha|29|03|2011}}
| categoría-Commons = Casa de las Alhajas, Madrid
| imagen = Casa de las Alhajas (Madrid) 02.jpg
| nombre = '''[[Ensanche de Madrid|Palacete tipo promovido por el Marqués de Salamanca en el Ensanche]]'''
| nombrecoor = Inmueble en la calle Villanueva, 18
| lugar = Calle de Villanueva, 18<br />28001 [[Madrid]]
| lat = 40.422437 | lon = -3.687604
| fecha = {{fecha|21|03|2012}}
| categoría-Commons-defecto=Cultural heritage monuments with local protection in the Community of Madrid
| categoría-Commons-auxiliar=1860s buildings in Madrid
| categoría-Commons-auxiliar1=Neoclassical buildings in Madrid
| categoría-Commons-auxiliar2=Mansions in Madrid
| categoría-Commons-auxiliar3=Buildings in Recoletos neighborhood, Madrid
| imagen = Calle de Villanueva nº 18 (Madrid) 01.jpg
- If there is a value for 'categoría-Commons', it must override any existing auxiliary category. That is, auxiliary (and default) categories must be considered if and only if 'categoría-Commons' does not exist or is empty.
However, at the moment, we're in the process of filling the category parameters in the monument lists. Most of them may be empty yet.