In I Will Bear Witness: A Diary of the Nazi Years, Klemperer constantly refers to "LTI." LTI is Lingua Tertii Imperii.
Lingua Tertii Imperii is part of a title translated as Language of the Third Reich. Klemperer's book Lingua Tertii Imperii: Notizbuch eines Philologen came to be highly respected and continues to be studied by linguists and historians today.
The book discusses a study, completed by Klemperer, which details the way Nazis "altered the German language" in order to instill certain Nazi ideas in the minds of the Germans.
The text is a collection of Klemperer's diary pages where he wrote about the language the Nazis created in order to give the words scientific connotations and take away from the realistic and common knowledge of what the word meant.
On a side note, Lingua Tertii Imperii: Notizbuch eines Philologen was originally published in 1947 (Germany). An English version was last published in 2006 by Continuum under the name Language of the Third Reich: LTI: Lingua Tertii Imperii.