Thanks for the reply musicmaster
I did not explain myself very well and this was the key.
I wanted to say: "When I import the combinations again in Spanish, if you delete the previous combinations, then it imports it well."
I have already detected the problem.
To avoid problems I must follow these steps:
1- import the products in English from "store 1"
2- import the products in Spanish from "store 2"
3- import the combinations in English from "store 1"
4- import the combinations in Spanish from "store 1"
If I do not proceed in this way (and import combinations in spanish from store 2), then prestashop create translations of the attributes with different id and they do not relate to each other. For example, the "XXL" value of the "size" attribute, in English it has id 5 and in Spanish id 8.
Maybe there is an easier way, but at the moment it is the only one I have found