I started Ehud Ben Zvi's A Historical-Critical Study of the Book of Zephaniah. I blogged about the introduction to this book a while back: see here.
What captured my attention was something that Ben Zvi said on page 29. After discussing the lack of interest in Zephaniah throughout the history of biblical interpretation, Ben Zvi noted that interest has increased in recent times (and this book by Ben Zvi dates to 1991). What has intrigued some people in the United States is "the supposedly African origin of Zephaniah..." I wondered what exactly gave people the impression that Zephaniah was from Africa, and, fortunately for my curiosity, Ben Zvi interacts with this issue in his discussion of Zephaniah 1:1.
Zephaniah 1:1 affirms that Zephaniah was the son of Cushi, the son of Gedaliah, the son of Amariah, the son of Hizkiah. Zephaniah was the son of Cushi. Cush in the Hebrew Bible can mean Nubia, or Ethiopia (see here). So that's where some have gotten the idea that Zephaniah had African origins.
Ben Zvi is open to the possibility that the other names were added after that of "Cushi" in order to demonstrate that Zephaniah came from a strong Judahite, Yahwistic line. Ben Zvi states on page 42 that the superscription concerning Zephaniah is unusual, for "Zeph 1:1 is the only superscription in the Latter Prophets in which a list mentioning five generations occurs." Plus, the sheer number of Yahwistic names in that particular superscription is anomalous, for "lists of three consecutive names ending with [yah] occur rarely in the OT" (page 49). For Ben Zvi, one should account for these anomalies, and one way to do so is to maintain that someone added names after "Cushi" to identify Zephaniah with Judah and with Yahwism. Ben Zvi still thinks that Cushi is a personal name rather than an indication of African nationality, for "this name is well attested epigraphically in West Semitic languages" (page 50). But, even if Cushi were the name of a person, someone could misunderstand and conclude that Zephaniah was a Cushite---and so someone came along and added some names to Zephaniah's lineage.
Unlike some, Ben Zvi does not think that the "Hizkiah" of Zephaniah 1:1 is King Hezekiah. Some have made that identification, arguing either that Zephaniah was a part of the royal family, or that someone tried to make Zephaniah appear to be so---in order to solidify his connection with Judah and Yahwism. According to Ben Zvi, one scholar, G. Rice, has tried to have the best of both worlds: to see Zephaniah as one with Cushite background, and also as a descendent of King Hezekiah. For Rice, Hezekiah married an Ethiopian woman and named his son from that union "Cushi" in order to acknowledge the country of origin of the child's mother. Rice argues that this would explain why Cushi marks a break in Yahwistic names in Zephaniah's genealogy.
But Ben Zvi disagrees, for the Peshitta reads that name as "Hilkiah," which may point to the existence of another reading in Hebrew manuscripts, plus there is no acknowledgment of any connection between Zephaniah and Hezekiah in places we would expect it---such as the "Lives of the Prophets" in Babylonian Talmud Megillah 15a.
The attempt to connect Zephaniah with Judah may be due to Judahite nationalism, or perhaps it reflected also a degree of prejudice against the Cushites. (Such prejudice is not present in many other parts of the Hebrew Bible, which are actually quite positive about Cush. Isaiah 18:7 may be one such example. Also, a Cushite rescues Jeremiah in Jeremiah 38.) Ben Zvi does not explicitly assert that Zephaniah's genealogy was expanded on account of prejudice, but, on pages 44-45, he refers to Jeremiah 36:14, which mentions Jehudi, the son of Nethaniah, the son of Shelemiah, the son of Cushi. Ben Zvi acknowledges the possibility that Jeremiah 36:14 is trying to portray Jehudi as the third generation from Cushi---since Deuteronomy 23:8-9 only permits children of Egyptians from the third generation and beyond to enter the congregation of the LORD, and some may have applied that rule to Nubians as well. Ben Zvi does not think that such an explanation is suitable for Zephaniah 1:1, but perhaps Deuteronomy 23 may contain a clue as to why there was an attempt to dissociate Zephaniah from Nubia---if there indeed was such an attempt.