I long for a language which has a basic featureset, and then "freezes", and no longer adds any more language features.
You may continue working on the standard library, optimizing, etc. Just no new language features.
In my opinion, someone should be able to learn all of a language in a few days, including every corner case and oddity, and then understand any code.
If new language features get added over time, eventually you get to the case where there are obscure features everyone has to look up every time they use them.
Common Lisp seems to tick the boxes. The syntax is stable and it doesn't change. New syntax can be added through extensions (pattern matching, string interpolation, etc). The language is stable, meaning code written in pure CL still runs 20 years later. Then there are de-facto standard libraries (bordeaux-threads, lparallel,…) and other libraries. Implementations continue to be optimized (SBCL, CCL) and to develop core features (package-local-nicknames) and new implementations arise (Clasp, CL on LLVM, notably for bioinformatics). It's been rough at the beginning but a joy so far.