The law is as follow:
1) No Nazi symbolism outside of a historic context. 2) No inciting racial hatred. 3) No expression of hatred against a protected minority (the wealthy are not a protected minority).
These are very easy to prove, but none of them apply to normal left wingers. There are Islamist left wingers that fall into these categories because of their anti-semeticism or anti Christian sentiments.
4) No denying crimes against humanity.
This DOES apply to left wingers. If you deny Stalin's genocide against the Ukrainians that would be illegal. It also equally applies to holocaust deniers. I don't know how often it comes up though.
5) No speach which undermines democratic values and seeks to opress others.
I don't think that this is ever actually used. Though it might apply against left wingers.