May one say the names of saints of idolatry, such as Paul/Peter/Patrick/Francis?
From the letter of the law, one may say their names without mentioning their status of sainthood. Thus, while one may say Paul/Patrick in reference to the apostles, one may not say a preface to his name which connotes reverence, such as Saint Paul. One is also not to write such a preface of reverence, and possibly should not even write its initial, such as S. Peter, because people may come to read it in full. [It however may be written for learning purposes, as stated earlier in the Q&A.] Furthermore, it is proper to mention their names in a derogatory form [when possible], such as Peter should be called Peter Chamur. [According to Chazal, Paul and Peter were Tzaddikim who were planted into the christian world in order to divert their religion away from resemblance to Judaism, and they remained faithful to the Jewish people throughout their lives. Nevertheless, they are still to be called by a derogatory name.]
May one say the name of a city that is named after an idol or Saint?
From the letter of the law, it is permitted to do so if the city is named after a saint. It is likewise permitted to say the name if the city is named after an idol whose name does not connote a deity and is used as a name of people or items, as stated above. Nevertheless, G-d fearing Jews are accustomed not to say the name of such cities but rather give it a nickname. For example, the city of Bela Tzurkav in Russia they would call Shevartza Tzurkav. If the city name is of a false deity whose name connotes a deity in the language originated, and is not used as a name of people or items, then [from the letter of the law] it may not be used to call the name of the city. [An example of such a city is perhaps Mumbai, which is the name of a pagan goddess which connotes the term “Mother of creation.” One should call it Bombay or another name of the like.]
Saying the word Saint of the city name: If the name is preceded by the term Saint, such as S. Diego, S. Paul, S. Monica, and the like, then it is not to be said or written even in initials, as stated in the previous Halacha. [The city of S. Monica is commonly called Simcha Monica by Chassidim. Nevertheless, when writing the name of a city in Gittin, one is to write the name as required by Halacha, even if it involves writing the preface of S.]
 Beis Yosef 147/2 in name of Rabbeinu Yerucham “However their Kedoshim/saints may be called by their names if they are names of people, although to call them by their names in a manner of reverence is forbidden.”; See also Michaber 147/2; Kneses Hagedola 147/4, brought in Darkei Teshuvah 147/7; See Likkutei Sichos 26/429 [printed in Shulchan Menachem 4/34-35] “Mentioning their names, even with a preface does not border the prohibition of “Lo Sazkiru”, as their name is not a name of Avoda Zara.” Nonetheless, a preface should not be mentioned.
 Likkutei Sichos 26/429 [printed in Shulchan Menachem 4/34-35] that one may not say the term Saint, and therefore there is a question if one should even write the initial S., let alone the actual word, lest people come to say it.
 Likkutei Sichos ibid that Rebbe questioned whether the letter S. may be written before the name, even if it is the name of a city, such as S. Petersburg, and the Rebbe referred the asker [who was a Tanya printer in such a city] to a Rav. Practically, the name published in that Tanya does not contain the S. [See Shulchan menachem ibid footnote 1]
 Sefer Chassidim 191 [Mosad Rav Kook-censored from some versions] “Even a Tzaddik who they make into a deity it is a Mitzvah to call a derogatory name, for example Shimon Kipah should be called Peter Chamur”
 See Sefer Chassidim ibid that Peter was a Tzaddik; See Rashi Avoda Zara 10a which was censored and brought in Dikdukei Sofrim Avoda Zara p. 12 footnote 9 “The Gemara states that all the writings and language of the nations is not from them. This means as follows: All of their books of heresy Yochanon Paulus [Paul] and Petrus which were Jews wrote. They purposely infected their culture in order to sway the Christian faith away from Judaism. They themselves were not heretics and did so for the benefit of the Jewish people, as written in the book Teliya Yeshu” Seemingly this refers to the book Toldos Yeshu, which brings the history of Yeshu from a Jewish perspective and writes how Peter infiltrated the ranks of Yeshu and turned away Christianity from being a threat to Judaism. Peter was appointed by the Sages to do so. For the full story in all details see: Sefer Toldos Yeshu [dating back to at least times of Rashi]; Beis Hamidrash vol. 5/60 and vol. 6 [1860; Likkut of old Midrashim] Midrash brought in Otzer Hamidrashim p. 557 [1920, by Rav Y.D. Eizanshtein]
Fast day of 9th of Teves: See Hagahos Baruch Frankel and Toldos Yeshu “On the 9th of Teves Shimon Hakalfus who helped save the Jewish people died and the Sages established it as a day of fasting”; See also Michaber 580/2 “On the 9th of Teves we do not know what Tzara happened”; See Taz 580/1 and M”A 580/6 who say Ezra died and question Michaber. However see Tur, Bahag; Orchos Chaim, Birkeiy Yosef who write that the Sages did not write what happened and it is left a mystery, and the fact Ezra died is not the reason for the fast. Accordingly, the words of Toldos Yeshu and Baruch Frankel reveal the secret that on this day Shimon Hakalfus died. Shimon Hakalfus was none other than Shimon Kifa, whose Christian name was S. Peter. He was the first Bishop/Pope of Rome and all the other popes are considered his inheritors.
Author of Nishmas: See also Siddur Avodas Yisrael, in name of an old manuscript siddur from the year 1407 “I heard from Yehuda Bar Yaakov that Shimon Ben Kipa authored Nishmas until the words Mi Yidmeh Lach” However see Machzor Vitri p. 282 Mahadurah Makitzei Nirdamim “Some say Nishmas was authored by the abomination of Rome, called Shimon Peter Chamor, which authored this liturgy and others while in the cave. Vechas Veshalom to say such a thing, and one who says so will have to bring a fat offering when Moshiach comes” Vetzaruch Iyun, as elsewhere in Machzor Vitri it states that Shimon Kipa authored the Piyutim of Seder Avoda said on Yom Kippur.
 Sefer Chassidim ibid regarding Shimon Kipa who was a Tzaddik that he should be called Peter Chamur
 The reason: As it is permitted to say names of idols that are also names of people, as brought from Poskim ibid, and the same would apply if these names are also names of cities. This allowance certainly applies if the name is merely that of a worshiper of idolatry and not an actual idol. [See Likkutei Sichos 26/429 [printed in Shulchan Menachem 4/34-35]
 See Likkutei Sichos 26/429 [printed in Shulchan Menachem 4/34-35]
 See Likkutei Sichos ibid that Rebbe questioned whether the letter S. may be written before the name, even if it is the name of a city, such as S. Petersburg, and the Rebbe referred the asker [who was a Tanya printer in such a city] to a Rav. Practically, the name published in that Tanya does not contain the S. [See Shulchan menachem ibid footnote 1]
 See Likkutei Sichos 26/429 [printed in Shulchan Menachem 4/34-35]; See Shulchan Menachem ibid footnote 5 regarding the wording of the city name in a Get written in Bela Tzurkav, that they used this name even though the Jews avoided calling it by this name, and rather gave it a derogatory term.