Using this as a point of departure, note the languages Holmes grants to the beginning Elf character:
Elves can speak the languages of orcs, hobgoblins and gnolls
Given that orcs are elves twisted beyond recognition suggests that the reason that elves know the language of the orcs is because it is a dialect of elvish. It follows that so, too, are the languages of the hobgoblin and gnoll. This suggests that hobgoblins and gnolls are either other twisted elves or a further twisting of orcs.
This vision is reinforced by the languages given the beginning Dwarf character:
Dwarves can all speak the languages of gnomes, kobolds and goblins.
Holmes essentially calls gnomes chaotic good hill dwarves:
Gnomes are similar to dwarves, whom they resemble. They are smaller, have longer noses and beards and inhabit low-land and hill burrows rather than mountains.
Kobolds are also described as a kind of dwarf:
These evil dwarf-like creatures behave much like goblins, but are less powerful.
The goblin behavior in question suggests that goblins, too, are a kind of dwarf:
They always attack dwarves on sight.
In other words, gnomes are chaotic dwarves, goblins are evil dwarves as are kobolds (possibly even a derivative of gnomes, due to their size). Therefore, the languages given the beginning dwarf character are likely all dialects of the original dwarven language.
This all suggests a very interesting definition of goblinoid, given how Holmes describes the hobgoblin:
Hobgoblins are big, powerful goblinoids
Since the suggested origin of hobgoblins is the elf and the suggested origin of the goblin is the dwarf, the term goblinoid seems to mean any race whose origin is the twisting of a progenitor race (such as elves or dwarves).
Given this statement by Holmes:
At the Dungeon Master's discretion a character can be anything his or her player wants him to be.
it follows that should one want to play a gnome, goblin or kobold that one could simply use the dwarf class as a template and, likewise, orcs, hobgoblins and gnolls could use the elf class as a template.