TOM MARVOLO RIDDLE
which is then rearranged into
I AM LORD VOLDEMORT
I'm well aware of the difficulty in translating idioms literally from one language to another, but anagrams present a whole new level of challenge. So I was both surprised and impressed when I read the book in Spanish (a very excellent translation, by the way) and the character's name was changed just enough to make the anagram work in the new language:
TOM SORVOLO RYDDLE -> SOY LORD VOLDEMORT
Of course, it's a fortunate coincidence that the word "I am" in Spanish lends itself easily to such a minor alteration. I started wondering about other languages. In German, would the translator find a way to work the letters of "Ich bin" into some similar variation of the name? Not quite; the phrase is changed slightly to read "Ist [Is] Lord Voldemort", rather than "I am..." and accordingly, the name becomes "Tom Vorlost Riddle".
Here is a table of translations into other languages; there are apparently quite a few in which this trick is preserved. In the Vietnamese edition I found at my local library, however, both parts of the anagram are left in their original English form, with the translation of "I am Lord Voldemort" given in a footnote. This, despite the fact that Vietnamese uses, more or less, the Roman alphabet; perhaps the translator couldn't come up with a similar-enough Vietnamese phrase, or perhaps it didn't occur to him that he could change the name as others had done. I haven't been able to lay my hands on a translation into a non-alphabetic language (e.g. Chinese) but I imagine there that the footnote method is the only way to go.