By my count 20°E passes through 19 countries.
We can do better than that :D
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I'm going to say 35 deg E, maybe passing through tonnes of East Europe/Balkans and then eastern Africa.
I think Schmenke and Storm are close. So I will day 25 east, through the middle of Europe and Africa
26 east
26°E also passes through 20 countries.
20 is good but wait, there's more.
27 east, trying to get Lesotho as well as South Africa to score 21
Slightly odd question - What time is it at the South Pole?