Update (Jan. 26): See our series on "God is Love, in past papal documents"; and, after the release of the official text on January 25, check TRANSLATION PROBLEMS OF THE LATIN TEXT OF DEUS CARITAS EST and its mistranslations.
The great Vaticanist Andrea Tornielli reports today in Il Giornale that the last corrections to the [Latin] text of the encyclical Deus caritas est were made last Monday and that the translations were finished only yesterday -- which is why the text will not be released this weekend, but really only on January 25, as the Pope himself confirmed today. This is just one aspect of the embarrassing Latin language problems in the Vatican staffs, highlighted by Alessandro Renzo in this other article (the low point of this was, of course, the Synod of Bishops, whose final propositions had to be issued in Italian, for fear of grave errors if the texts were made known in the language of the Church).
Tornielli reports that the first part of the encyclical, on the theology of Divine Charity, has been written by the Pope himself; the second part, dedicated to "charity" in a broader sense and to the charitable activities of the Church is a recycling of an old project of an encyclical on charity which had been planned for John Paul II but which had been considered unsatisfactory and whose text had been archived.
This double authorship has apparently been the reason for the translation problems, since both texts had to be "harmonised" before the Latin text was considered apt for translation. The last revision, this very week, was naturally also verified by the Pope.