Especially on StackOverflow, but also in the Embarcadero forums, I frequently encounter (stupidly) written DLLs, e.g. for hardware or some exotic piece of software that expose things like C++ classes or Delphi AnsiStrings or dynamic arrays. It should have been obvious that such DLLs can not be used by most users who use another language to communicate with the DLL.
That is why I wrote an article called "DLL dos and don'ts" about how I would write DLLs that can be consumed by (almost) every language. I think that it could be a good read for anyone writing DLLs, not just for Delphi users.