Answer - The treatise was translated into Hebrew in the 16th century, long before the maskilim came into existence. Fragments of the original Arabic, dating probably from the 14th century, were discovered in the Cairo Geniza. The treatise has been printed in the Ein Yaakov for a long time, without anyone challenging it as being heretical. In any case, Rabbeinu Avraham's point was also stated by Rav Hai Gaon, Rambam, Rav Hirsch, and others. For further discussion, click here.
Question - "Rabbi Moshe Shapiro further claims that the letter of Rabbi Samson Raphael Hirsch discussing Chazal and science was not written in Hirsch's handwriting and is a forgery. Is this true?"
Answer - On Thursday, November 11th, 2004, I spoke with Rabbi Dr. Mordechai Breuer, one of the greatest living experts on Rav Hirsch, who published the letters in HaMaayan. He told me that there is absolutely no doubt whatsoever that they were originally written by Rav Hirsch and copied by his family members. Furthermore, the letters were written as part of a correspondence with R' Hile Wechsler, whose letters have been published. R' Wechsler was clearly under the impression that he was corresponding, as he frequently did, with Rav Hirsch.