TOP TEN OF THE LONGEST WORDS IN DIFFERENT LANGUAGES

ARABIC
15 letters
 أفإستسقيناكموها (’af’astsqynakmwha, "did we ask you to give it to us to drink").

ENGLISH
45 letters
pneumonoultramicroscopicsilicovolcanoconiosis a supposed lung disease  

CROATIAN
30 letters
 long prijestolonasljednikovičičinima (lj is considered a one letter in Croatian alphabet). Translation would be "of little heiress apparent to the throne" 

 DANISH
51 letters
 Speciallægepraksisplanlægningsstabiliseringsperiode, has been used in an official context. It means "Period of plan stabilising for a specialist doctor's practice," and was used during negotiations with the local government.

ESTONIAN
31 letters
 One other long word is uusaastaöövastuvõtuhommikuidüll at 31 characters, denoting an ideallistic morning after the new year. It can be used in a sentence such as
 Maalilist jõuluööeelootusaega ja illuminaarses aoõhetuses uusaastaöövastuvõtuhommikuidülli  
to say "merry Christmas and a happy new year".

FINNISH
61 Letters
 entokonesuihkuturbiinimoottoriapumekaanikkoaliupseerioppilas "airplane jet turbine engine auxiliary mechanic non-commissioned officer student"

GERMAN
65 Letters
 siebenhundertsiebenundsiebzigtausendsiebenhundertsiebenundsiebzig (777,777)

SPANISH
54-letters
 pentakismyriahexakisquilioletracosiohexacontapentágono ("56645-side polygon"). Other long words are "Pneumonoultramicroscopisilicovulcanoconiosis" 

RUSSIAN
46 letters
 Тысячевосьмисотвосьмидесятидевятимикрометровый (Tysyachevosmisotvosmidesyatidevyatimikrometrovy), which is an adjective meaning "1889-micrometer"
  
POLISH
168 Letters
Dziewięćsetdziewięćdziesiątdziewięćmiliardówdzięwiećsetdziewiędziesiątdziewięćmilionówdziewięćsetdziewięsiątdziewięćtysięcydziewięćsetdziewiędździesięciodziewięcioletni means "999,999,999,999 years old").