Please introduce at Kolab Roundcube plugins a calendar week in calendar views "Week" and "Month" as suggested in the screenshots. First suggestion is "Month" by introducing just a small column before the first existing column:
Second suggestion is "Week" where the calendar week information can simply be put into the currently empty cell (e.g. "KW 35" in German, "CW 35" in English):
(moved from https://github.com/roundcube/roundcubemail/issues/6377, creating a "feature request" failed with: Task priority "20" is not a valid task priority. Use a priority keyword to choose a task priority: unbreak, triage, high, normal, low, wish.)