A Google script to dynamically change the data validation rules based on the selection from another cell.

french_time_dropdowns.js

function onEdit(){
 
  const ss = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  const entries = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("entries");
  const dropDowns = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("dropdowns");
  const activeCell = entries.getCurrentCell();
  const activity = activeCell.getValue();

  if(activeCell.getColumn() == 3 && activeCell.getRow() > 1){
    activeCell.offset(0,1).clearContent().clearDataValidations();
    if(activeCell.isBlank()) {
    }
  
  const dropDownValues = {
   Conferences: "B2:B10",
   Classes: "C2:C10",
   Excursions: "D2:D10",
   Tutoring: "E2:E10",
   Workshops: "F2:F10"
}; 

  const rangeData = dropDownValues[activity];//frenchValues(dropDownValues,activity);
  const getValueRange = dropDowns.getRange(rangeData)
  const confValidationRule = SpreadsheetApp.newDataValidation().requireValueInRange(getValueRange).setAllowInvalid(false).build();
   
  activeCell.offset(0,1).setDataValidation(confValidationRule);
   
  }
}