Composite primary key for 1-to-many relationship? - sql

Question

Well, I was always doing it like this:
create table language (
id bigserial primary key,
code varchar(10) not null
);
create table entity (
id bigserial primary key
);
create table entity_description (
id bigserial primary key,
language_id bigint not null,
constraint fk__entity_description__language
foreign key language_id
references language(id),
entity_id bigint not null,
constraint fk__entity_description__entity
foreign key entity_id
references entity(id),
name varchar(20) not null
);
but I wonder.. why wouldn't I do it like this:
create table language (
id bigserial primary key,
code varchar(10) not null
);
create table entity (
id bigserial primary key
);
create table entity_description (
language_id bigint not null,
constraint fk__entity_description__language
foreign key language_id
references language(id),
entity_id bigint not null,
constraint fk__entity_description__entity
foreign key entity_id
references entity(id),
primary key (language_id, entity_id),
name varchar(20) not null
);
My questions are
Is there anything that speaks against the composite primary key in the second example?
Are there any benefits?
Are, in the second example, (language_id, entity_id), language_id and entity_id indexed separately for table entity_description? If I fetch for .. WHERE entity_description.id = x is this slower than fetching for .. WHERE (entity_description.language_id, entity_description.entity_id) = (x,y)?