After doing the Bediqath Hamess (search for leaven) at night, one should nullify all Hamess (leaven) that may have remained in one's possession, by reading the first "Kol Hamira" (all leaven that is in my possession...should become nullified).
The nullification process, as ordained by the Torah, can be done in one's heart, but the Hakhamim ordained that we should should actually utter the words, and the one reciting it must understand what he is saying. Someone who does not understand the language in which it is written (Aramaic) should recite it in the language he understands.
If someone who does not understand Hebrew or Aramaic recites it in one of those languages and does not understand at all what he is saying, thinking he is reciting some kind of a prayer or request, he has clearly not fulfilled his obligation at all. However, in the event that he knew what he was reciting but did not understand the actual words, he has fulfilled his obligation aposteriori.
(See Shulhan 'Arukh, 434: 2. Rema, ibid. Kaf Hahayim ibid, Oth 19, 32-33.)
