1Hi all,
in Spain "testimonial, controversial, etc.. are always translated, if not it´s considered a wrong translation, as it has a different meaning:
In fact, testimonial means true:
testimonial.
(Del lat. testimoniālis).
1. adj. Que hace fe y verdadero testimonio.
2. f. pl. Instrumento auténtico que asegura y hace fe de lo contenido en él.
3. f. Testimonio que dan los obispos de la buena vida, costumbres y libertad de un súbdito que pasa a otra diócesis.
I feel the best translation, always depending on the context, could be "recomendaciones" when is a client`s opinion about a product or service, or "testimonios" when is about a witness testifying, evicences, a History writer or an official document -the notar for instance, gives "testimonio" with his/her signature of the authentication of a document-. Also out of Juridic sector, is also used when people write about something that they want to maintain or be known by others "dejar testimonio escrito".
Hope this helps, and please correct my English.
Nicka ;D.