The month of July is, on average, the cheapest month to fly to Strasbourg from Ireland, with most prices found around 142€. If you aren’t able to travel during the month of July, then book flights to Strasbourg from Ireland during September instead. Flights to Strasbourg in September, while not as cheap as those in July, still average around 143€.
Those flying to Strasbourg could potentially find better pricing at Mulhouse EuroAirport (110 km from Strasbourg city centre), Metz Metz-Nancy-Lorraine Airport (120 km from Strasbourg city centre) or Épinal Mirecourt Airport (127 km from Strasbourg city centre), depending on the month and departure airport.