I don't think it says anything nasty, AFAICT that was Wirth's approach to languages in general: they were all meant to be modified and extended for each platfor

I don't think it says anything nasty, AFAICT that was Wirth's approach to languages in general: they were all meant to be modified and extended for each platform and need. Even his own implementations had extensions to accommodate what it needed to do (e.g. IIRC his Oberon-07 implementation for ARM had some additional data types). Besides in practice in the last ~3 decades or so every implementation was based on Borland's dialect (which AFAIK was based on the UCSD dialect). Also FWIW Free Pascal is both open source and has a mode to compile code in standard Pascal, though it was added relatively recently (version 3.0.0 released in 2015 - i wrote "relatively" because the compiler exists since the mid-90s).