In file app/helpers/timelog_helper.rb
I've patched two methods do not correctly display the decimal format, because they aren't reading general_csv_decimal_separator. Here are the new methods I've patched:

def report_to_csv_with_td_csv(criterias, periods, hours)
  decimal_separator = l(:general_csv_decimal_separator)

  export = FCSV.generate(:col_sep => l(:general_csv_separator)) do |csv|
    # Column headers
    headers = criterias.collect {|criteria| l(@available_criterias[criteria][:label]) }
    headers += periods
    headers << l(:label_total)
    csv << headers.collect {|c| to_utf8(c) }
    # Content
    report_criteria_to_csv(csv, criterias, periods, hours)
    # Total row
    row = [ l(:label_total) ] + [''] * (criterias.size - 1)
    total = 0
    periods.each do |period|
      sum = sum_hours(select_hours(hours, @columns, period.to_s)) 
      total += sum
      row << (sum > 0 ? ("%.2f" % sum).gsub('.',decimal_separator) : '')
    end
    row << ("%.2f" %total).gsub('.',decimal_separator)
    csv << row
  end
  export      
end

def report_criteria_to_csv_with_td_csv(csv, criterias, periods, hours, level=0)
  decimal_separator = l(:general_csv_decimal_separator)

  hours.collect {|h| h[criterias[level]].to_s}.uniq.each do |value|
    hours_for_value = select_hours(hours, criterias[level], value)
    next if hours_for_value.empty?
    row = [''] * level
    row << to_utf8(format_criteria_value(criterias[level], value))
    row += [''] * (criterias.length - level - 1)
    total = 0
    periods.each do |period|
      sum = sum_hours(select_hours(hours_for_value, @columns, period.to_s))
      total += sum
      row << (sum > 0 ? ("%.2f" % sum).gsub('.',decimal_separator) : '')
    end
    row << ("%.2f" %total).gsub('.',decimal_separator)
    csv << row

    if criterias.length > level + 1
      report_criteria_to_csv(csv, criterias, periods, hours_for_value, level + 1)
    end
  end     
end