Thank you very much.
And regarding foul language jokingly between friends (like “bastard,” etc., where there is no intention to hurt or insult and the other side is not offended),
is there a halakhic prohibition, or is it simply improper?

There is no clear halakhic prohibition. Maybe “do not make yourselves detestable.”

Forgive me, I’m just having a bit of trouble understanding the prohibition of cursing.
“Whoever curses a judge from among the judges of Israel violates a prohibition, as it says: ‘You shall not curse God,’ and if he cursed the nasi, one who is head of the Great Sanhedrin or the king, he likewise violates a prohibition, as it says: ‘And you shall not curse a leader among your people.’
And not only a judge or a nasi, but whoever curses any one of Israel is flogged, as it says: ‘You shall not curse the deaf.’”
Maimonides goes on to ask: if every person is included in the biblical prohibition, why does the Torah mention specifically the deaf person? And he answers his own question: “For even this one, who does not hear and was not distressed by this curse, one is flogged for cursing him.” That is, even when the victim of the curse is unaware that he was cursed, the curser still commits the transgression in full severity.
Maimonides writes this, and it is ruled likewise in the Shulchan Arukh: “whoever curses any one of Israel.”
Does this have no connection to curses in TV series, plays, or joking curses between friends?

This is a great example of the confusions created by modern Hebrew. There is no connection at all between the concept of a curse in Jewish law and foul language. A “curse” in Jewish law means wishing harm in God’s name. There is no prohibition here against foul language.

I understand, thank you very much.
What about the claim by rabbis who quote the Shulchan Arukh and say that it is forbidden to watch any series at all because it contains violence, and violence arouses the evil inclination?

I see no point in responding to every piece of nonsense someone blurts out.