How can I display the number of items per category in the Django admin filter panel?

In Django admin, how could I add the number of items for each category of a filter directly in the filter panel (see mock-up below)?

Current filter panel

Desired filter panel

Model

I am filtering my UserProfile table by its languages field. This is a many-to-many field on the Language table.

class UserProfile(models.Model):
    # ...
    languages = models.ManyToManyField(Language, blank=True)

class Language(models.Model):
    name = models.CharField(max_length=64)
    # ...

My current admin configuration is:

@admin.register(UserProfile):
class UserProfileAdmin(admin.ModelAdmin):
    # ...
    list_filter = ('languages',)

This should work:

class UserProfileLanguageFilter(admin.SimpleListFilter):
    title = _('Language')
    parameter_name = 'languages'

    def lookups(self, request, model_admin):
        qs = model_admin.get_queryset(request)
        # Return a list of (id, name) for lookups. We return the language_id and the string format "Language Name (Count of Users)" as the name.
        return [(i, "{}({})".format(j, k)) for i, j, k in
                qs.values_list('languages__id', 'languages__name').annotate(
                    user_count=Count('userprofile')).distinct().order_by(
                    'languages__name')]

    def queryset(self, request, queryset):
        if self.value():  # Use the lookup id we sent above; to filter
            return queryset.filter(languages__id=self.value())


@admin.register(UserProfile):
class UserProfileAdmin(admin.ModelAdmin):
    # ...
    list_filter = (UserProfileLanguageFilter,)

I'd definitely encourage you to understand the Filter and also the Queryset better, if you choose to pick up code directly.