Actually, lots of things are formal. Statements in mathematics, assuming all parties agree on notation and convention, is formal. It's quite easy to decide if, for example, a statement in first-order logic is well-formed (correctness is another issue altogether, and as we know no formal axiomatic system can be consistent and complete).

To me, it's a contradiction to say "x isn't a formal language with a decision procedure for well-formedness" and "A is/isn't a well-formed statement in x."