Actually, I have doubt, As Microsoft claim that .net support around 60+ programming languages, so my question is that do all those Programming languages have their own libraries along with the base class library or they all consume the base class library.
if they are having their own libraries than what is the use of BCL
if they are using BCL then all those languages will have different syntax.
Both. All .Net languages have access to the BCL, but typically there is also some additional language-specific libraries to support common idioms in the language.
For example F# has the FSharp.Core library: https://fsharp.github.io/fsharp-core-docs/ with support for F# specific types and utilities.