Word for Thursday in European Languages

It's Irish and Scottish Gaelic. Wednesday was also a fast day in early christianity. This disappeared from Western tradition, but still observed in Eastern Ortodoxy.

You are right, originally they did. The answer is catholicism happened:

A religious purist, Jón made it his mission to uproot all remnants of paganism. This included changing the names of the days of the week. Thus Óðinsdagr, "day of Odin", became miðvikudagr, "mid-week day" and the days of Týr and Thor became the prosaic "third day" and "fifth day".

In this case it's likely of Muslim origin, as iberia was under muslin domain for a long time and lots of Arabic names were behind.

Borrowed from Old Swedish þōrsdagher, from Proto-West Germanic Þunras dag (“day of the thunder god”).

https://en.m.wiktionary.org/wiki/torstai

It's pretty literally just T(h)or's day. But how they turned Freya's day into perjantai is pretty baffling.

Well, that's the ISO standard, so if you think otherwise, you are wrong :)

[D] is the weekday number, from 1 through 7, beginning with Monday and ending with Sunday.

https://en.wikipedia.org/wiki/ISO_8601#Week_dates

Actually some of the former British colonies and most of the Americas start the week on Sunday, Muslim World start on Saturday, Maldives on Friday, rest of the planet follows the standard.

https://en.wikipedia.org/wiki/Week#/media/File:First_Day_of_Week_World_Map.svg

Yeah, that's how it is for all the countries/languages colored purple on the map

Hey ,it is reasonable it is the fourth day so let's call it the fourth day.

I mean the last 4 English month names are basically <#>month, but never got updated when the Romans switched from a 10 month calendar to a twelve month calendar. The suffix -ber comes from the latin word for month, with the prefix being the Latin number Septem = 7, Octo = 8, Novem = 9, Decem = 10. The two new months (January and February) were inserted at the start of the year throwing the naming off by 2.

July and August were originally called Quintilis and Sextilis so the 5th and 6th months and renamed after the calendar change, to honour Julius and Augustus.

This map is not about a nation's word for Thursday but about the word in different languages. Austria for example isn't labelled with any word because Austrians speak German and the German word for Thursday is already placed in Germany. The English word Thursday is placed in England, its most logical location. The Gaelic word for Thursday meanwhile is placed in Scotland, its most logical place. This doesn't imply that the majority of Scottish people speak Gaelic, only that Scotland is the country with the highest number of Gaelic speakers while England has the highest number of English speakers in Europe.

Political maps are a terrible tool for visualizing cultural / linguistic practices (and on this one, colonization didn't make it even worse). Just gotta roll with it and enjoy the weird assumptions :)