I find the comments misleading (maybe because i'm not english native) but

if (daysTo < -1) {
      switch (date.dayOfWeek()) {
      case 1:
          return tr("Last Monday",    "day in the previous week");
      case 2:

Why does it have to be the previous week? If today is Wednesday and the date we're referring to is Monday, daysTo will be -2 and it will still be the current week and not the previous, no?

else if (daysTo > 1) {

switch (date.dayOfWeek()) {
case 4:
    return tr("Next Thursday",  "day in the week after this");

If today is Monday and the date we're referring to is Thursday, daysTo will be 3 and it's not "the week after this" it's "this week".

Or am i understanding something wrong?