Fortran

Many Fortran programs are based on older codebases that may not be well-documented or well-maintained. Maintaining and updating these systems can be difficult and error-prone.

Integrating Fortran with other languages or systems can be complex. Although there are tools and methods for interoperability (such as using Fortran with C or Python), it often requires additional effort and expertise.

For new programmers or those transitioning from more modern languages, Fortran’s syntax and idioms can be challenging to learn, especially given its different approach to things like array handling and control structures.

Even with updates in Fortran 90 and beyond, some modern programming paradigms and features (like advanced object-oriented programming or functional programming) are either not well-supported or are implemented differently.

While Fortran has strong libraries for scientific computing, its overall ecosystem is smaller compared to more modern languages like Python or C++. This can limit the availability of third-party tools and libraries.

Older versions of Fortran have outdated syntax and features that can be cumbersome compared to modern languages. Although Fortran 90 and later versions introduced many improvements, older codebases may still use outdated constructs.