Once again, The Language Factory has produced an extremely useful month-by-month infographic which collates and summarises key national holidays and 'dates to avoid' across 11 countries.
Invaluable for planning international work, you simply hover over a date and the infographic tells you whether it is a national or local holiday. The infographic shows what day of the week the holiday will fall on, along with information about the holiday itself and whether a bridging holiday is likely to be taken by those who celebrate it. This should give you an indication of when services are likely to be reduced and when it might be more difficult to conduct market research in these countries.