What does Genesis 35:23 mean?
The previous verse concludes with a statement that Jacob—named Israel by God (Genesis 32:28; 35:10)—had 12 sons. This and the following verses (Genesis 35:24–26) list those sons according to their birth mothers. Jacob intended only to marry Rachel, but was tricked by her father into also marrying her sister, Leah (Genesis 29:25–28). The rivalry between the sisters played out, in part, in bearing children (Genesis 29:30–31). This included enlisting their servants as concubines. The children born to Leah's servant, Zilpah (Genesis 35:26), would have been considered Leah's from a legal standpoint.The sons of Jacob's unloved wife, Leah (Genesis 29:30–31) include, in order, Reuben (Genesis 29:32), Simeon (Genesis 29:33), Levi (Genesis 29:34), Judah (Genesis 29:35), Issachar (Genesis 30:17–18), and Zebulun (Genesis 30:19–20). These will become 6 of the 12 storied tribes of Israel.
It's all but certain these women had other children, but only the sons of Jacob are noted here. Dinah is also a child of Leah, only mentioned by name due to her abuse by a local prince (Genesis 30:21; 34:1).