Houyhnhnm language

(?) - approximate, guessed

Yahoo - a barbaric humanoid; evil; having worse or poor quality; human (?) : Part 4, Chapter 1 (4,1)
Houyhnhnm - horse; perfection of nature; a sentient horse from an island south of the Australian coast : 4,1
Hhuun - attend [to him] : 4,1
Hnea-Yahoo - the Yahoo's evil; a disease (?) : 4,7
Ylnhiamshy - aborigines, natives : 4,8
Ihnuwnh - to return to a first mother; to die : 4,8
Hhnm Yahoo - the folly of a servant : 4,9
Whnaholm Yahoo - the loss of a child : 4,9
Ynlhmndwihlma Yahoo - a stone that cuts their feet (?) ; continued bad weather (?) : 4,9
Ynholmhnmrohlnw Yahoo - a poorly-built house : 4,9
Nnuhnoh - a small mammal that is as large as a rabbit that is hunted for its fur : 4,10
Hnuy illa nyha majah Yahoo - take care of thyself, gentle Yahoo : 4,11

The Houyhnhnm language is based on the neighing of horses.

Laputan language, and Barlnibarbian and Luggnaggian as well

Laputan:

Lap (archaic) - high
untuh (archaic) - governor
Lapuntuh (archaic) - high governor, modernized as "Laputa"; the name of the flying island
Lagado - capital city
Flandona Gagnole - Astronomer's Cave
Balnibarbi - a continent located under Laputa
Munodi - a governor in Laputa
"Tribnia" (invented) - Gulliver's anagram for "Britain", a nation of informers
"Langden" (invented) - Gulliver's anagram for "England"

Balnibarbian:

Ickpling gloffthrobb squut serumm blhiop mlashnalt zwin tnodbalkuffh slhiophad gurdlubh asht - May your celestial majesty outlive the sun eleven moons and a half
Fluft drin yalerick dwuldom prastrad mirpush - My tongue is in the mouth of my friend; I need to bring my interpreter
bliffmarklub - high chamberlain

Luggnaggian:

Luggnagg - an island east of Japan
Maldonada - a large port in Luggnagg
Glubbdubdribb - an island of sorcerers and magicians
Clumegnig - a river that flows along the southeastern point of Luggnagg
Traldragdubb, Trildrogdrib - a port in Luggnagg
struldbrug -an immortal with a red mark on his forehead who becomes incapable on activity upon reaching old age
slumskudask - an item given by a struldbrug to ensure that the receiver remembers him
Glanguenstald - a port in southwestern Luggnagg, that functions as its only link with Japan

Brobdingnagian language

(?) approximate, guessed

Brobdingnag - (name of a country) : not mentioned
Grildrig - a tiny man : Part 2, Chapter 2 (2,2)
Glumdalclitch - a little nurse : 2,2
splacnuck - a six-foot long animal : 2,2
grulrud - town crier : 2,2
Lorbrulgrud - Pride of the Universe : 2,2
Slardral - gentleman usher : 2,3
relplum scalcath - freak of nature, unrestrained person
glomglung - a unit of measurement; three glomglungs correspond to 54 English miles (86.9 kilometres) : 2,4
Flanflasnic - a city "within eighteen English miles of the seaside" (28.97 kilometres) : 2,8

Russian vulgar slang (part 1 - Warning: NSFW topics)

(Many of these words can be very inappropriate in most settings, or just too offensive to be used. Be careful!)