The most straightforward real language in terms of syntax seems to be C.
I'm not sure what you mean by "real language", but whatever "real language" means, I cannot agree that C has a "straightforward" lexical or syntactic grammar, and its semantics are underspecified. If you want an extremely straightforward language with pretty well-defined semantics, why not go for Scheme? Scheme has a very easy grammar but is certainly not trivial to get its semantics right.
