This is one we discussed at a bit of length and could have gone with either. Consensus was to use James. We will likely also teach the word "Seumasaich" (Jacobites) at some point and it will probably help to have people associate the term with James or at least be aware of the link.
This is the cultural practice in Gaelic. A Gaelic speaker known as Oighrig in Gaelic would be Effie in English. The situation is very different than say with French or Spanish names. Someone known as Seumas could potentially be known as either Seumas or James. We have tried to reflect actual cultural practices as accurately as possible. We also talk about this in the course notes if you would like to read further.