Comment COBOL (Score 1) 257
Actually...25 years ago was 1990. Windows 3.0 had just come out.
I worked on a project once that used three programming languages. All three of them had gone through incompatibility-causing changes by the end of the project, and that in a space of three years. One was C; it went from 16 bits to 32 (which should tell you when this was). Since I was doing things that depended on the size of int (I was using ints--or maybe it was long ints--to encode things at the bit level), that was relevant. That would not have been too hard to fix. The second language was Prolog; the version I used also transitioned to 32 bits, and the vendor decided at the same time to change the way C calls were made. That would have been more difficult to change in my code. The third language was Smalltalk; the vendor was bought out by its competitor, who had an incompatible version. The version we used was dumped. That would have been a nearly complete re-write.
As a result, my next project encoded its information in XML, and I wrote a converter (in Python) to translate the XML to the programming language of a finite state transducer. When (not if) that transducer becomes obsolete, we'll change the converter. (Of course Python may go out in 25 years, but the converter is the simple part.) I do not expect XML to go obsolete soon, and when it does, at least the data is human-readable (and there will probably be a converter to whatever the replacement for XML is).