Somehow the subject of Yiddish names came up recently. Although I expect many readers to know all about this, it also seems that many do not realize quite the way they used to be perceived. Today it is not uncommon for a boy to receive a name like Zalman at his bris, but in the past this was almost never what happened. A boy who would be called Zalman, or even Shlomo Zalman, was invariably given the name Shlomo. This became known as his shem kodesh the holy - Hebrew - name, and when he grew up it was the name he'd be called to the Torah with. Some time after the bris there might be a small ceremony where he'd be given the name Zalman, which is what he would actually be called. This name was the shem chol, the secular or pehraps better, daily - name.
This was an old Ashkenazic custom going back to early medieval times; certainly in some places there may not have been a ceremony, but they just started calling the baby by the Yiddish, or German, or Judeo-German equivalent of the Hebrew name. It was known as "chol kreisch," which I guess means something like "calling of the secular [name]," although it must be pointed out that it is spelled "Hollekreisch" in Latin letters, and some pesky scholars conjecture that it refers to a female demon called Holle or Hulda who was active in bothering babies in German speaking lands many centuries ago. See M. Guedemann ספר התורה והחיים בארצות המערב בימי הבינים vol. II (Warsaw 1898) p.85 (link). It must be noted though that as early as the 15th century the term was explained by a rabbi as referring to chol in the sense of secular - see Maharam Minz (#19). While this cannot fully refute the previously mentioned conjecture, surely it is notable that this was asserted in the still demon-haunted middle ages. Besides, the Jews had their own baby demon, Lilith. Actually I think that fact can be used to support either conjecture.
The ceremony continued into recent times, and perhaps still continues (as opposed to being resurrected by Neo-Ashkenazim, as undoubtedly it also has). Here for example is the "liturgy" to be recited at such a ceremony as printed in Seligmann Baer's Seder Avodat Yisrael (Roedelheim 1868):
As an example of the two-name phenomenon, although I do not claim that these represents cases of a ceremony, many medieval Asheknazic rabbis were called Leon, and are referred to as "Rabbi Leon" in the literature. Some are sometimes called Rabbi Yehuda or Aryeh and the like, so we plainly see that at least some of them had both names. In all likelihood the Hebrew name was what they were named at the circumcision, while Leon was what they were called on a daily basis, no different from the "Leib" of later time. For example, the rebbe of Rabbenu Gershom was named Rabbi Leon (sometimes Leontin). See Maharam Rothenburg (#264): "ר' ליאון רבי שלמדני רוב תלמודי זצ"ל חכם מופלא."
No one really thought of these names as anything more than nicknames. They were not holy Jewish names. Naturally, however, an entire literature developed around the proper spelling - and origin - of these names, since when writing gittin - divorce documents - halacha requires precision even in spelling. See for starters Beit Yosef Even Haezer 129, where the spelling of names, including Leon, is discussed (this is only the tip of the iceberg for this literature).
As an illustration of this, here is the title page of a book from 1789:
This collection of R. Mordechai Halberstadt's responsa was published posthumously by his grandson, who included some of his father's own original Torah insights as well, under the title Lechem Eden. The title page informs us that the name of these are derived from a word play on his father's name: "ששמו הקודש מנחם ושמו החול מענדל מכוונים בתיבות הללו," "For his holy name, Menachem, and his secular name, Mendel, are intended by these words."