why do people create a standard(or specification) for every language soon after its developed?
C++
In 1998, the C++ standards committee (the ISO/IEC JTC1/SC22/WG21
working group) standardized C++ and published the international
standard ISO/IEC 14882:1998 (informally known as C++98).
Java
In 1997, Sun Microsystems approached the ISO/IEC JTC1 standards body
and later the Ecma International to formalize Java, but it soon
withdrew from the process.
JavaScript
In November 1996, Netscape announced that it had submitted JavaScript
to Ecma International for consideration as an industry standard, and
subsequent work resulted in the standardized version named ECMAScript.
and the list goes on.
Primarily to assure that different implementations agree on what actually constitutes the language, and therefore what they accept and reject in programs written in that language.
This is largely driven by the fact that early on, many languages (e.g., Lisp) were not standardized, which led to fragmentation and incompatibility.