I should double-check the documentation of the time package.
.Date.Day refers to the nth day of the month, whereas
.Date.Weekday corresponds to the nth weekday.
December = Null happened because weekdays have a zero-based index, whereas months are counted (intuitively) from one upwards.
Overall, the snippet is nearly the same as the one for the translations of month names that has been linked in the introductory post. It was mentioned that
wochentage.toml is a data file. Maybe it wasn’t as obvious that it belongs in the
data/ folder but the next time I’ll try to be more precise in the details