In the Iberian Peninsula at least the name was originally spelt
Mafalda. It was introduced by the Italian
Princess Mahaut (Maud/Matilda) of Savoy, who married
Afonso Henriques, the first king of Portugal in 1146. A number of her descendents carried the name, including an granddaughter who married the king of Castile and was later beatified.
The latinate form
Matilde only became common centuries later, by
German influence I believe. Oddly enough both
Mafalda and
Matilde are very popular in Portugal nowadays.