Hi Jesús,
Yeah, in fact I solved the issue by changing that column in the database. I've noticed also other problem: in the very same import some Subject Access Points were created twice: one row for english language (source_culture = en) and another row for the spanish language (source_culture=es). That would be nice if it worked properly, but it isn't. The spanish row name for the subject access point is NULL. So, I've found records like this:
id = 1 | name = "SUBJECT_EXAMPLE_NAME" | source_culture="en"
id = 1 | name = NULL | source_culture="es"
id = 2 | name = "SUBJECT_EXAMPLE_NAME_2" | source_culture="en"
id = 2 | name = NULL | source_culture="es"
So I had to fill those NULL names with name column found in their english translation. This issue only happens sometimes. As I've stated before, most rows inserted only once (with source_culture=en).
Thanks for your help, if you need more info about the bug, please feel free to contact me again.