But DE, SE, and ES are the official two-digit ISO 3166 country codes for Germany, Sweden, and Spain, respectively. The ISO 3166 country code for Greece is GR, not ES.
However, el is the official ISO 639 language code for the Greek language (lowercase, not uppercase!). So for some reason, someone decided to use the uppercase Greek language code to denote the country of Greece. (the two-digit ISO 639 language code for Sweden is sv, so it’s not even consistent)
As /u/Successful_Try543@feddit.org pointed out, they apparently use the VAT identification number for this image.
Ah, yes, the horseshoe.
I wouldn’t consider BSW as a classical left-wing party, though (also rejected by BSW, but I think smaller/new parties usually try to avoid classifying themselves in the left-right-spectrum). Sociopolitically, their positions appear (not much substance so far) to be more closely align with the conservative-/right-wing-end of the political spectrum.