So I do it also. The system of wikitree is based on the american convention of names with its "middle name". In the former Germany they used the system of two given names. In my village, Glauberg, County of Stolberg-Gedern, now Hessen, D, 80 % get the Name Johann Henrich (later Heinrich), Johann Georg, Johann Daniel, Johann Peter and so on. 10 % had the name Johannes (without a sevond name!). In the time of 1728-1854 children most get the given Name of the "Pate", Soma had two Paten, so their given Name had been mixed.
Girls had as first Name "Anna" (about 80%) between 1728-1854 and as second name Maria, Catharina, Eva, Barbara and so on.
In the marriage and death registry often only the second Name had been documented (so the "Anna" and the "Johann" wasn't used!).
So I use to note both names in the field "first name", the other field I do not fill, the question of the system "No second name" I say yes.
PS: my village has been "evangelisch", men and women, who married to this village often hat names, that ahdn't been given in my village. So, in catholic villages or in other villages, they used perhaps other cenventions.