You`ll need to do Oposiciones courses and exams for all public employment, this includes Guardia Civil, Policia Nacional and Local and Bombero`s.
You can read criteria and info here.
http://www.oposiciones.de/default.htm
Has subsections to each of the Guardia,Nacional and Local.
You`ll need your exam results translated to Spanish and if not acceptable you`ll need to sit Spanish Exams.
This is the requirements for Guardia Civil ;
Requisitos:
Ser espa?ol.
Tener cumplidos 18 a?os y no cumplir ni haber cumplido 30 a?os en el a?o de la convocatoria.
Tener una estatura m?nima de 1,70 metros los hombres y 1,60 las mujeres.
Acreditar buena conducta ciudadana.
No estar privado de derechos civiles.
No haber sido condenado por delito doloso ni separado del servicio del Estado, de la Administraci?n auton?mica, local o institucional, ni hallarse inhabilitado para el ejercicio de funciones publicas.
Estar en posesi?n del permiso de conducir de la actual clase B, antes B1.
Estar en posesi?n o en condiciones de obtener, antes de la primera prueba, el t?tulo de Graduado en Educaci?n Secundaria, Formaci?n Profesional espec?fica de grado medio, 2? BUP, Formaci?n Profesional primer grado o equivalente.
No tener adquirida la condici?n de objetor de conciencia.
In English;
Requirements:
Be Spanish.
Be age 18 years and not comply with or having attained 30 years in the year of the summons.
Women have a minimum height of 1,70 metres men and 1.60.
Accredit conduct citizen.
Not be private civil rights.
You have not been sentenced for crime fraudulent or separate from the service of the State, regional, local or institutional, management or find disabled for the exercise of functions public.
Be in possession of from driving the current class B, before B1.
Be in possession or conditions obtain, before the first test, the title of graduated in secondary education, medium grade-specific training 2nd BUP, vocational training first degree or equivalent.
The status of conscientious objector have not acquired.
If your from a non Spanish speaking country, you`ll also need to show formal qualifications in Spanish language, from what I`ve been told, it will need to be at least Degree level.
You may also be able to transfer from a Police service in an EU country into Spain.
They have done it for citizen's of South American countries as well.