How language designers decides whether to use compiler or interpreter??

Answer 1

Languages are actually independent of the implementation method (compiled, interpreted). It is common for people to label Python as interpreted, Java as compiled, etc, but in fact any language can either be compiled or interpreted. As such, "interpreted languages" and "compiled languages" are terms which are not well defined.

Sample discussion on C++ interpreters:
https://stackoverflow.com/questions/69539/

Compiling Python code:
https://stackoverflow.com/questions/471191/

Putting that aside, I think what you really wanted to ask was this:
https://www.quora.com/Why-do-we-use-interpreters-instead-of-using-compilers-for-everything-Is-platform-independence-the-main-reason

Answer 2

Thank you :) Fermi