Composition and "separating interface from implementation" are not specific to OOP languages.
Composition has been used since LISP I and ALGOL 60 in almost all programming languages.
"Separating interface from implementation" is also the main feature of the programming languages based on abstract types, starting with Alphard and CLU, which are not OOP languages and which predate the time when Smalltalk has become known to the public, launching the OOP fashion.
An abstract type is defined by an interface, i.e. by a set of functions that have arguments of that type and this is a programming language feature that is completely independent of the OOP features like member functions, virtual functions and inheritance.
All OOP languages have some kind of abstract types, though with a different point of view on the relationships between individual objects and types a.k.a. classes and the functions that operate on them, but there have been many languages with abstract data types without the OOP features.
Moreover "separating interface from implementation" has also been the main feature of all programming languages based on modules, starting with Mesa, Modula and Ada.
The features that identify an OOP language are the idea that the functions belong to individual objects, not to types, hence the member functions, the substitution of the union types (of the right kind, like in Algol 68, not of the pathetic kinds encountered in Pascal and C and derived languages) with virtual functions (to provide an alternative form of dynamic polymorphism, which is preferable for closed-source software, by allowing changes without recompilation, unlike with tagged unions where there are select/case/switch statements that must be recompiled when the union is extended), and the inheritance in a class hierarchy.
There are many languages that are multi-paradigm, like C++ or D, where you can choose whether to write a program in an OOP style or in a totally different style, but there are also languages where it is difficult to avoid using the OOP features, or even impossible, because all the available data types may be derived from some base "object" type, inheriting its properties.
Composition has been used since LISP I and ALGOL 60 in almost all programming languages.
"Separating interface from implementation" is also the main feature of the programming languages based on abstract types, starting with Alphard and CLU, which are not OOP languages and which predate the time when Smalltalk has become known to the public, launching the OOP fashion.
An abstract type is defined by an interface, i.e. by a set of functions that have arguments of that type and this is a programming language feature that is completely independent of the OOP features like member functions, virtual functions and inheritance.
All OOP languages have some kind of abstract types, though with a different point of view on the relationships between individual objects and types a.k.a. classes and the functions that operate on them, but there have been many languages with abstract data types without the OOP features.
Moreover "separating interface from implementation" has also been the main feature of all programming languages based on modules, starting with Mesa, Modula and Ada.
The features that identify an OOP language are the idea that the functions belong to individual objects, not to types, hence the member functions, the substitution of the union types (of the right kind, like in Algol 68, not of the pathetic kinds encountered in Pascal and C and derived languages) with virtual functions (to provide an alternative form of dynamic polymorphism, which is preferable for closed-source software, by allowing changes without recompilation, unlike with tagged unions where there are select/case/switch statements that must be recompiled when the union is extended), and the inheritance in a class hierarchy.
There are many languages that are multi-paradigm, like C++ or D, where you can choose whether to write a program in an OOP style or in a totally different style, but there are also languages where it is difficult to avoid using the OOP features, or even impossible, because all the available data types may be derived from some base "object" type, inheriting its properties.