"Mankind" to refer to all humans.
"All men are created equal" to refer to all humans.
"No one shall be arbitrarily deprived of his nationality nor denied the right to change his nationality" refers to all humans.
More recently as other comments have pointed out, singular "they/their" has become more accepted. "No one shall be arbitrarily deprived of their nationality nor denied the right to change their nationality".
Actually, singular "they" predates generic "he" by several centuries. Generic "he" was an 18th-19th century invention.
[1]: https://en.wikipedia.org/wiki/Third-person_pronoun#Generic_h...
The singular they[1] has precedent going back to the fourteenth century. Just use that.
I wish people who felt about that strongly and wanted to make a political statement just used the gendered she creating the fictional world where only girls exist. That would have been so much simpler and avoided so much pointless arguments over the grammatical number and gender of pronouns.
Also, in Swedish we have ”he/she/* = han/hon/hen”. Which is soo useful and I am still kind of amazed that the term ”hen” is a relative modern invention. I wonder how in earlier days people referred to other people when the gender was not the main focus. Maybe it was always more important before? Or was perhaps the use of titles (the Dentristess..?) a way to denote gender an important communication tool?