Villarreal leading 2-0 against Zenit at home and combined 5-1. No way are they going out now. So at least 3 out of the 16 remaining European teams will be Spanish. Sevilla (Munir) just scored a golazo (a beautiful volley outside of the penalty area) and there will be extra time should the current result (2-2) stand until the end of the 90 minutes. Could be 4 out of 16 (25%) which as written earlier won't be too bad in the worst season in almost 1 decade for Spanish teams in Europe.
In any case Sevilla's away form is truly something else in a negative way.
Eintracht leading 0-1 against Inter and they might end up being the only German team left. Talk about a bad season from the German teams. Ligue 1 not doing much better. Might have 0 teams left should Rennes go out as expected.
Italian teams, unfortunately, not doing good either. Potentially only Juve and Napoli left after tonight.
So potentially 4 Spanish teams, 6 English teams, 2 Italian ones, 1 Dutch one, 2 Portuguese team (or 1 depending on whether Zagreb manages to qualify so far 1-0 in the return leg) and finally 1 German team (Eintracht) if they do not go out which looks unlikely so far.
If Sevilla go out they have only themselves to blame for. Creating more chances this time around as well and should already have been qualified securely without much trouble. Unfortunately this is not how football works like and they might very well be kicked out. Slavia Prague are not as bad as one would believe and from what I can see (UEFA's Coefficient Ranking), the Czech league is one of the better leagues in Europe. Currently ranked 13th while Slavia Prague are leading the Czech league.
https://kassiesa.home.xs4all.nl/bert/uefa/data/method5/crank2019.html