Most puzzles and questions asked on CodeGolf are interesting and challenging. However, usually the answers that win are created from pre-fabricated languages designed for golfing code. This seems unfair since it is easy to make ANY language you like for any situation. Languages used to answer these questions are not "Real" languages. They are made for a specific purpose to reduce code size. A symbol used in a golfing language needs to represent a built-in function. At university, we made an artificial language using Java. I believe answers in CodeGolf should be from mainstream/real languages...this would show real skill.
You're not allowed, to make a random language, to solve a specific challenge
We have things called "forbidden loopholes". One of them is, that a language can't be made to only include one specific builtin, for a specific challenge, and it must had a compiler before the challenge was posted. This makes it impossible to create artificial languages for specific challenges.
Your suggestion has already been implemented. Only real programming languages are permitted to enter challenges on this site. What constitutes a real programming language for this site is defined here on meta.
Note that this rules out some languages which are designed only for a small number of specific tasks. Languages which are designed to be terse still need to meet all of the requirements for being a real programming language.
Most of the golfing languages you see on this site are real programming languages, some of which are actually used outside of the golfing context (several of our users use CJam for scripts unrelated to PPCG). If you spot a language that does not meet our definition, raise it on meta so the community can verify whether or not it counts as real.