Very simply, encore has here the common meaning of still. Encore can have this particular usage where it shows that although a certain progress has been made on a particular concept, it is still not enough to be satisfactory.
(In the quoted example: Although these texts present diverse interests, they are still too influenced by marxist concepts)
Having seen the context provided by OP, I would rephrase the quoted example like the following: Although the second volume texts present diverse interests, the first and even the second ones are still too influenced by the marxist terminology.
I agree with N. Labrahmi that “encore” = “still” here, but I think that it is possible that the reviewer could be referring, not to the first two texts under review, but all the way back to W. G. Sebald’s first collection of essays (La description du malheur) to express his/her opinion that the collection currently being reviewed (Amère patrie) unnecessarily [still] contains essays that rely too heavily on Marxist concepts.
It’s interesting, perhaps even relevant, to note that whereas La description du malheur was published in 1985 (just as Mikhail Gorbachev began hinting in May of that year at the need to implement Glasnost and Perestroika in earnest and four years before the demolition of the Berlin Wall and ensuing German reunification), Amère patrie was published in 1991 (two years after the Wall’s fall and very near the dissolution of the Soviet Union in December of that year).
This could mean that “encore=still” was used here, not necessarily to express that the reviewer was personally against [reading about] communism or Marxist concepts in general, but rather to express, in light of what had transpired in the Soviet Bloc between 1985 and 1991, that “still” including [too many] essays from the Marxist point of view in a 1991 collection, was perhaps questionable and/or distracting.
(see the entire review from juanasenio.com for the respective dates of publication of the two essay collections and for the basis of my interpretation of what “encore” might mean in this case)