You wrote:A number of numerical libraries in Java can be found at JavaNumerics
"Modern" in this context means to me: object oriented (not C or Fortran)
Fortran has object-oriented features since 2003, see, for instance Fortran working group note 5
IMHO (IMHO object-orientation has been oversold, in general, and does not belong in Fortran, specifically, but the Fortran standards committee didn't ask me, alas)
Commercial libraries that have been ported to Fortran 2003 include IMSL and NAG. Opensource library LAPACK is F90, but if you are going to do numerical work, chances are, you'll have to use it.
A software library in a "modern" programming language could attract more people (maybe more contributors if it is open source), for this reason, than a library in a much better suited, but less known, programming language.
It is much harder to write robust numerical code, than to contribute to an average opensource project. I believe, that the choice of language is a tertiary concern, - understanding the mathematical subject matter and error anlysis takes more work than learning another (procedural) programming language.