Delphi is based on Object-Pascal and for more almost 30 years is in the heart of many application you use daily. For various reasons, although Delphi was dominant in the 90's and early 00's, the use of Delphi declined and other languages and frameworks started taking its place, without necessarily being better or more efficient.
Delphi is not a dead language, it is actively developed from Embarcadero, which took over Borland. Legacy code written in older versions Delphi can be migrated with minimal changes to the latest version of Delphi.
Delphi is also a valid choice for new projects: it can be used for desktop applications for various platforms, mobile applications, cloud-based applications and much more. It has also considerable advantages over its competitors (C#, Java, etc): It produces native binaries, its deployment is very easy and you can target multiple platforms with the same code.