[struwwelpeter]

I guess it's not just German that likes to make up huge words:

(Translation:)
KavkazChat - the longest word! (game)
Rentgenehlektrokardiograficheskogo - 33 letters
('of x-ray electrocardiographic').

That's not really a Russian word, since the roots are German. How about these:

(Translation:)
1. The longest word in the Russian language, though not registered in the dictionary:
Vodogryazetorfoparafinolechenie; ('water-mud-parafin treatment')
2. Longest word in the Bulgarian language consists of 39 letters and means 'Do not disrupt the constitution', and looks like this:
NEPROTIVOKONSTITUTSIONSTVUVATELSTVUVAYTE;
3. Newspaperman Bruce LaBruce in one of his articles asserted that there is no longer word in modern English than 'antidisestablishmentarianism', but one of his readers disagreed and sent in his collection of letters:
Pneumonoultramicroscopicsilicovolcaniosis;

[shhrubbery!]

Hey, my ancestors the Swedes do agglutinative words too:

NORDÖSTERSJÖKUSTARTILLERIFLYGSPANINGSSIMULATORANLÄGG- NINGSMATERIELUNDERHÅLLSUPPFÖLJNINGSSYSTEMDISKUSSIONS- INLÄGGSFÖRBEREDELSEARBETEN.

This means "preparatory work on the contribution to the discussion on the maintaining system of support of the material of the aviation survey simulator device within the north-east part of the coast artillery of the Baltic."

[Getready]

But the "pneumono..." word is a technical word, i.e. it
is part of medical terminology...so it's not in general
use....some of the other foreign words mentioned in some
of the previous posts seem like those that can be
used in non-technical settings.