It's definitively not the source of the word, but it might very well be the reason the decided to have a "fest i val". Gothenburg is famous for their puns, and even today they open up the mouth of the whale for visitors on two occasions - valdagen (election day) and Valborgsmässoafton (Walpurgis eve).
> From Middle English festival (adjective), from Old French festival (“festive”), from Late Latin fēstīvālis, from Latin fēstīvus (“festive”). By surface analysis, festive + -al. Displaced native Old English frēols. The noun is shortened from festival day, from Middle English festival dai, festiuall day (“feast day, festival”).
It surely is; 'fest' is the Swedish word for 'party'. I actually think Swedish or Norwegian (which are practically the same language) are closer to English than even Dutch. Many of the most common, short English words are the same.
The Anglo-Saxon migrations made England English, and then the waves of Viking invasions littered North Germanic vocabulary all over it. You can see it in doublets like skirt/shirt that aren't in other West Germanic languages.
"Fest" is also German for celebration - but just because several Germanic languages have the same word doesn't mean that it's a Germanic word. Actually all of them got it from Latin...
I should have checked the etymology, but the way this reply is worded is a bit nitpicky. English did not loan 'fest' directly from Latin.
Edit: Though I realise now I misunderstood the original comment re: 'i val'. I took it to mean 'fest' only. No, I don't think 'party in whale' is the root of 'festival'
The word can be deconstructed in Swedish as fest i val which translates to "party in whale"