In Spanish, the concept of "spin-off" is known as "something that is imitative or derivative of an earlier work, product, or establishment; especially: a television show starring a character popular in a secondary role of an earlier show", but the English term is used for that purpose. So, in Spanish we can say:
Better call Saul es un spin-off de Breaking Bad.
See this example from the Spanish press:
La televisión norteamericana nos ha acostumbrado a las secuelas, las denominadas "spin-off", sobre todo en el género de la telecomedia, donde es frecuente que personajes secundarios de una serie se conviertan a su vez en protagonistas de otras [...].
La Vanguardia, 15/09/1994.
In that example the word secuela is used, but according to the DLE, a secuela is a "work that continues the plot started in another work". But a spin-off do not necessarily needs to continue a previous plot, as they can also be prequels (as in the Better call Saul example), or just tell a completely new story using a character from a previous show.
So, is there a more Spanish way (other than secuela) to speak about the spin-offs, or is the English term widely accepted?