I haven't seen the "E" designation from B+W, it might be something made up by the vendor. There is an "EW" designation, but that's one of the mount types (F-Pro is the standard, XS-Pro is slim with front threads, etc.; EW is Extra Wide, which means the glass part of the filter is wider than the lens threads, e.g. a 77mm EW filter is an 82mm filter with 77mm threads, to avoid vignetting on UWA lenses).
From the translation, it seems to refer to the Käsemann CPLs, which B+W describes like this:
The “high-end” polarizing foils of the Käsemann-type filters are neutral in color, they have a higher efficiency than conventional polarizing foils and they are cemented between high-grade plano-parallel optical glass. The resulting sandwich is then precision-polished again to achieve highly accurate plano-parallel surfaces. Subsequently they are edge-sealed to protect the foil against humidity. Discriminating photographers regard the B+W Käsemann-Type Polarizing Filter to be the very best of all polarizing filters. They are well suited for applications that require the highest possible imaging quality, especially with high-speed telephoto lenses and apochromatic lenses.
The commonly-used Käsemann polarizers are MRC-coated; the ones that are only single-coated are the linear polarizers, the standard/slim mount CPLs that are 105mm in diameter and larger, and the EW mount CPLs that are 86mm diameter and larger.
Short version: the Käsemann CPLs are of higher optical quality than the regular CPLs, and in the commonly used sizes also offer the benefits of the MRC coating. The only downside is they cost more...