From what I understand, windows in Europe are very different than in the US - they don't slide open but swing, like doors. So an American window unit, which seals the window opening, is not feasible. They have portable units with air hoses, but I am also not sure how you can get such a hose out of a swinging window without leaving a big gap for the hot air to come back.
I see, all I found is a piece of cloth you tape around window opening though. I don't think it's doing a great job of insulation, and, paired with an inefficient portable unit, what kind of temperature difference can you get inside vs outside?
It's not the money. In many places you need to go through permitting to get it and they do not want to give it to you. Often you also need a signed approval from every person in the building.
There is something very wrong in the EU if installing a life saving window air conditioner requires a permit or signed approval from every person in the building.
This is true. In many places you can't install the outdoor unit on the street-facing side of the building without approval, and you won't get it in most cases, and this is indeed in addition to getting approval from your building's residents association if you live in a flat.