Full Idea
An obvious suggestion is that concrete objects are denizens of space-time, and hence subject to causality, though Hale objects that languages are plausibly abstract and yet undergo change and so presumably exist in time.
Gist of Idea
Perhaps concrete objects are entities which are in space-time and subject to causality
Source
E.J. Lowe (The Possibility of Metaphysics [1998], 2.10)
Book Reference
Lowe,E.J.: 'The Possibility of Metaphysics' [OUP 2001], p.51
A Reaction
The identity-conditions for a language are pretty loose. Choosing a counterexample from the mental life of human beings begs a billion questions. I can't think of a problem case beyond the world of human culture.