I LOVE self-made words! There should be a 2-25 dictionary one day, with all of the words that I've made up. [img]i/expressions/face-icon-small-tongue.gif[/img]

But back on topic, I just like to say that some things can be lost through translations. For example, jokes. Like in anime, the nose-bleeding reaction whenever some hot chick walks by, is equivalent to the "Wow, she's so hot that I'm drooling" western phrase.
Okay...that might not be the best example...
but what I'm trying to say is that sometimes, expressions or phrases in one language might not exist in another language.
Second shot of an example: there's this really funny Chinese idiom that directly translates in English as "playing piano to a cow."
Yeah... that just doesn't work in English.
So, it might be altered to "I'm talking to a brick wall" or something (with the meaning adjusted a bit even, but same attempt in humour).

Oh, and another point is that self- made words, like shamelessness, help further develop characters and add on realism to dialogues.
Example: "That is huge!"
changed to: "Wow, that's ginormous!"