There are many cultural differences between France and Ireland but let me tell you some of them:
Food: In France, we eat a lot of pasta and tacos. In Ireland it seems that people are more into French fries, chicken tenders and pizza.
I also think that French students cook more than Irish students. That is maybe because in France, we have a lot of cooking shows on TV, so French people learn how to cook by watching TV.
Hardly arrived in Sligo i had to fill the fridge so i had to go either at Tesco, Aldi or Lidl.
I noticed that there is a restricted choice of food but they are big fans of beef. We cannot find a lot of fish even if we are located on the coast. Also prices are very exaggerated. For example a jar of Nutella costs around 5 euros and a pack of cigarettes costs 11 euros . As a french guy i am fond of wine and cheese but i think you should bring some of them in your luggage like i did because it is authorized and you will not eat the only cheese named Cheddar and disgusting wines which taste like exported vinegar.
A mix of a sweet white wine, wild boar terrine, Salami, Duck foie gras, lump-fish roe, snails, blue cheese, Artisons cheese, Brie cheese, St Nectaire cheese, Goat cheese, Camembert cheese, Salers and Gaperon directly imported from France.
Pubs and Clubs: Pubs tend to open earlier and it is more usual to see Irish people drinking a beer or a tea in the afternoon than in France. Guinness is one of the finest and tastiest beer. the biggest Guinness storehouse is located in Dublin.
I was very disappointed about clubs that close at 2.30 sometimes 3 am instead of 6 am in France. At this time students prefer having house parties.
Dress code: In Ireland, everyone tends to dress the same way, while in France being fashion is being dressed differently. I also noticed that Irish people do not really care about being cold especially when they are going out at night.
At school, the majority of Irish students prefer to wear a tracksuit instead of wearing a jean or a dress even if it is cold.
Manners: This question is difficult because French people have a lot of manners. Basically, in France, you do handshakes or cheek kiss to greet someone. In Ireland you just say hello. Also I think that French people are more keen on keeping their house clean because they do not wear shoes inside.
Punctuality: Being on time is a real problem in Ireland even if it is normal to be 10 minutes or 1 hour late. Irish people tend to be cooler for that whereas in France, it is very bad considered to be 5 minutes late. However it is more appreciable when somebody arrives 10 minutes earlier. In Ireland this cannot happen.
Communication: Irish people are very friendly and they talk about anything at any time even in a pub or in the street contrary to France where people answer rudely or look at you like a pervert even if you ask for the time or your way if you are getting lost. Irish people are very open minded. Also, the dialog between students and teachers is not as formal as in France.
Pace of life: In France, students have class from Monday to Friday and sometimes on Saturday. In Ireland, students start their courses at 9 am and finish sooner. Usually their lessons end on Friday.