Questions about Mario Kart 8 Deluxe

For me it was the chip (the card, not the code)

The text on the box is multilingual (including english), the game itself is in whatever language your Switch is set to. Switch games are region free

Bought them with cassette, complete as in the picture

Depending on the purchase price, the sales prices then also differ. The digital variant is also configured as a direct third-party offer. Here we only sell the corresponding code and have no verified information on the required storage space. According to non-binding internet research and information at www.nintendo.com/store/products/mario-kart-8-deluxe-switch/, it should be around 7.4 GB.

Yes, you can. However, you need a Nintendo Switch Online membership.
This is subject to a fee. There are 2 types: individual membership and family membership.
This membership can be tested for 7 days (which I would do to test whether the interaction between the Switch and the online connection works properly).
The prices can be found on the Nintendo website.
I hope this information helps.
Have fun