TIMTOWTDI but here is a Schwartzian Transform approach.

#!/usr/bin/env perl 
use strict;
use warnings;

my @in = <DATA>;

my @sorted =
    map { "$_->[1]$_->[0]" }
    sort { $a->[0] cmp $b->[0] }
    map { s/^([oa] )//; [$_, $1 // ''] } @in;

print @sorted;

__DATA__
# Drink
a cerveja|beer
a laranja|orange
beber|to drink
o copo de vinho|glass of wine
o copo|glass or cup
o sumo|juice
[download]

Any modules useful for general languages learning and grammar?

Grammar is tough. Have you looked at the modules in the Lingua::PT space? Perhaps Lingua:PT::Conjugate might be one place to start? Good luck.

Update: Just spotted the copo de vinho was out of order so here is an improved ST:

#!/usr/bin/env perl 
use strict;
use warnings;

my @in = <DATA>;

my @sorted =
    map { $_->[1] }
    sort { $a->[0] cmp $b->[0] }
    map { /^(?:[oa] )?([^|]+)/; [$1, $_] } @in;

print @sorted;

__DATA__
# Drink
a cerveja|beer
a laranja|orange
beber|to drink
o copo de vinho|glass of wine
o copo|glass or cup
o sumo|juice
[download]