Create an abstract Enum class

Here's how to adapt the accepted answer to the question Abstract Enum Class using ABCMeta and EnumMeta to create the kind of abstract Enum class you want:

from abc import abstractmethod, ABC, ABCMeta
from enum import auto, Flag, EnumMeta


class ABCEnumMeta(ABCMeta, EnumMeta):

    def __new__(mcls, *args, **kw):
        abstract_enum_cls = super().__new__(mcls, *args, **kw)
        # Only check abstractions if members were defined.
        if abstract_enum_cls._member_map_:
            try:  # Handle existence of undefined abstract methods.
                absmethods = list(abstract_enum_cls.__abstractmethods__)
                if absmethods:
                    missing = ', '.join(f'{method!r}' for method in absmethods)
                    plural = 's' if len(absmethods) > 1 else ''
                    raise TypeError(
                       f"cannot instantiate abstract class {abstract_enum_cls.__name__!r}"
                       f" with abstract method{plural} {missing}")
            except AttributeError:
                pass
        return abstract_enum_cls


class TranslateableFlag(Flag, metaclass=ABCEnumMeta):

    @classmethod
    @abstractmethod
    def base(cls):
        pass

    def translate(self):
        base = self.base()
        if self in base:
            return base[self]
        else:
            ret = []
            for basic in base:
                if basic in self:
                    ret.append(base[basic])
            return " | ".join(ret)


class Students1(TranslateableFlag):
    ALICE = auto()
    BOB = auto()
    CHARLIE = auto()
    ALL = ALICE | BOB | CHARLIE

    @classmethod
    def base(cls):
        return {Students1.ALICE: "Alice", Students1.BOB: "Bob",
                Students1.CHARLIE: "Charlie"}


# Abstract method not defined - should raise TypeError.
class Students2(TranslateableFlag):
    ALICE = auto()
    BOB = auto()
    CHARLIE = auto()
    ALL = ALICE | BOB | CHARLIE

#    @classmethod
#    def base(cls):
#        ...

Result:

Traceback (most recent call last):
  ...
TypeError: cannot instantiate abstract class 'Students2' with abstract method 'base'

Here is a fix of the accepted answer for python 3.8. The only change is to the ABCEnumMeta. The rest is copy-pasted from the original answer to provide a runnable example. Also tested on python 3.6.2.

from abc import abstractmethod, ABC, ABCMeta
from enum import auto, Flag, EnumMeta


class ABCEnumMeta(EnumMeta, ABCMeta):
    pass


class TranslateableFlag(Flag, metaclass=ABCEnumMeta):

    @classmethod
    @abstractmethod
    def base(cls):
        pass

    def translate(self):
        base = self.base()
        if self in base:
            return base[self]
        else:
            ret = []
            for basic in base:
                if basic in self:
                    ret.append(base[basic])
            return " | ".join(ret)


class Students1(TranslateableFlag):
    ALICE = auto()
    BOB = auto()
    CHARLIE = auto()
    ALL = ALICE | BOB | CHARLIE

    @classmethod
    def base(cls):
        return {Students1.ALICE: "Alice", Students1.BOB: "Bob",
                Students1.CHARLIE: "Charlie"}


class Students2(TranslateableFlag):
    ALICE = auto()
    BOB = auto()
    CHARLIE = auto()
    ALL = ALICE | BOB | CHARLIE
    
# Abstract method not defined - should raise TypeError.
#    @classmethod
#    def base(cls):
#        ...