I don't know whether I'm relieved or disappointed that most of these don't work in the original French...
I am quite surprised that nobody mentioned Javert's "I ought to be punished"/"I deserve punishment" (whichever translations these are) yet... For once, this is even better in French "Je dois être puni".
Apropos translations: I recently picked up a rather old and incredibly dreadful German translation from 1932. The translator uses words and phrases that would have been considered archaic in the early 19th century and he cuts so heavily that sometimes half a sentence is missing. And his word choice is more than once really... suggestive (at least to somebody who speaks modern German).
Leading to the following gems:
Valjean's arrival in Digne: "An einem der ersten Tage des Monats Oktober (...) langte ein Fußwanderer zu der kleinen Stadt Digne hin." This is actually a mistake! "Hingelangen" can mean arrive (with the conotation of difficulty); "hinlangen" (the one the translator used) means "reach out", "grab", "help oneself". So it means: "A man grabbed (something) in the little town of Digne?" So what the heck was Valjean doing there?
After it is said that the husband of Valjean's sister died: "Er ersetzte den Ehemann völlig und unterstützte die Schwester, die ihn aufgezogen hatte" - "He substituted the husband entirely and supported the sister, who had raised him"
Javert confesses to "Madeleine" and tells him about how Champmathieu was arrested and brought to Arras: "Sehen Sie den Finger der Vorsehung?" - "Do you see the finger of providence?" So basically providence was telling them all to fuck off?
Three examples about how cutting half a sentence or even just one word can be really bad:
About Valjean earning 18 sous during pruning season and taking up all kinds of jobs outside the season: "Dann verkaufte er sich und tat was er konnte" - "Then he sold himself and did what he could". Maybe Valjean should have considered that way of making money...
Javert quotes Brevet as saying to Champmathieu: "Wir waren ja zusammen." (verbatim: "After all, we were together") There is no way that (at least nowadays) this sentence would mean anything but "After all, we were a couple."
(If he'd said "Wir waren ja zusammen dort" - "After all we were there together"; there's no way it could have been misunderstood!)
Javert questions Sister Simplice: "Sie haben heute abend keinen Mann gesehen?" - "You haven't seen a man tonight?"
And, the absolute best: Mme Magloire complains about the bishop letting Valjean stay in his house: "Einen solchen Mann aufzunehmen! Ihn mit sich schlafen zu lassen!" - "To take in such a man! To let him sleep with oneself!"