The language is selectable from the settings screen, the pictures in the review look like they have been lifted direct from the German manual.
The OAS instruments are normal computers inside, so any problems with VSTs will be the same as any PC computer.
The OAS software, Windows and all the standard samples (Including option packs) use about 600Mb of memory.
A lot of the processing for OAS is done by an OEM version of the Creamware 6 DSP cards (Pulsar 2) with scope ASIO drivers giving a default latency of 7ms. (Adjustable) http://www.creamware.com/index.php?submenu=products&seite=products&lang=en
All mixing, hardware connections and external in/Outs etc are done by a Wersi custom built programmable interface board.
As far as I can ascertain the VST Host is based on the VST Host produced by Steinberg.
OAS 7 adds multiple synthesis modules and so does not now have to rely on just samples. (All samples are still in a modified Creamware sts format)
The 6 editing features shown are specific to the voice, and are in addition to the standard editing features. As an example with the Piano one of the settings allows you to alter the hammer action, whereas the guitar has one for Fret noise adjustments etc.
Hope this helps

Bill