Old co-conspirator Dwight Peterson pursued the “James”/“Jacob” question more diligently than I, with some intriguing results. First, the translation “James” seems to have prevailed from the time of Tyndale and Wycliffe. Second, even the languages that don’t supply a starkly different form for the New Testament author tend to differentiate the Old Testament patriarch in some way: German “Jakob” OT, “Jakobus” NT; the Vulgate, “Iacob” OT, “Iacobus” NT. Likewise, he notes that the French Bible Jerusalem in his collection identifies the OT figure as “Jacob,” while the NT figure is “Jacques.” And of course, the New Testament and the Septuagint apply the name Ιακωβ (undeclined) to the patriarch (and to Jesus’ grandfather), but Ιακωβος (the declinable form) to all the companions of Jesus who go by this name.
Quite intriguing. It clearly makes no vast difference in most ways — an apostle by any other name would remain in the New Testament canon, even if the letter may be pseudepigraphical — but it suggests a lot about the role that presuppositions play in biblical interpretation. Even scholars who wear their non-theological identity proudly collaborate with the linguistic proclivity to mark a sharp rupture between the “Christian” James and the “Jewish” Jacob.