I was about to go nuts trying to figure out why I couldn’t enter an array for a VLOOKUP in Google Sheets. Quite a bit of Googling later it turns out that there’s BACKSLASH to separate arrays into columns – but only if you’re using a locale which uses a comma as number separator (instead of dot in the US/UK) and semi-colon for separating function values.

Thanks to https://www.benlcollins.com/spreadsheets/sheets-location/

TL;DR:
Google Sheets – lookup a date and return the weekday (as text, not as an integer).
=VLOOKUP(WEEKDAY(A1;2);{1\"Mon";2\"Tue";3\"Wed";4\"Thu";5\"Fri";6\"Sat";7\"Sun"};2;0)