The song used several times in the series, "Bella Ciao," is a partisan hymn, adapted from an old Italian country folk song from the latter part of the 19th century. During WWII, it represented the Italian resistance against Benito Mussolini. It is used worldwide as an anti-fascist hymn of freedom and survival in hard times. This tune has been re-recorded by many famous singers and translated into many languages. Even nowadays it can be found in protests and resistance situations around the world.
In season 1 when Arturito and Denver is in the vault fighting, Arturo mentions that his "son" that Monica is having wouldn't like Denver knocking on his door. However, it would be too early to find out the sex of the baby. Even if they did know it was a boy, the season 3 when Denver is surprised and excited to have a boy wouldn't make sense.
Also, in season 3, Arturito is talking to his fans about his poor son. If they are in hiding, then Arturito wouldn't know the sex of the child.
Further Details: The above is not a revealing error but actually a translation error. "Mi hijo" does mean "my son" in Spanish but it depends upon context. If the gender is unknown that "mi hijo" would therefore be correctly understood as "my child" and this should have been reflected in the translation. The original Spanish dialogue however, is in fact correct.
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