翻訳 - 英語 -フランス語 - Joseph Conrad

There's a mistake in the quotation, which explains why the English text doesn't make a lot of sense, and why it is next to impossible to translate it into French correctly. The key word is "HAPPINESS", which should be replaced by "LONELINESS". See now:

Who knows what true loneliness is – not the conventional word but the naked terror? To the lonely themselves it wears a mask. The most miserable outcast hugs some memory or some illusion.
– Joseph Conrad
http://kenfran.tripod.com/quotlist.htm#Conrad

Now it makes all the sense in the world and can be translated into French without any problem.