Have you ever had a relative correct you saying that your ancestor's "real name" was something other than what you have on the family tree or in your genealogical database? Maybe this real name is the name that appears on a baptism record or the one that they preferred to be called. Unfortunately, a name is not the same as a date. An ancestor's birth date is an immutable fact. Whether or not records are consistent or accurate, there is an objective birth date that can never change. Names are much more changeable and contextually-defined facts. I have a name that I use in official contexts and others I use in informal contexts. You may have a nickname that family uses, one that friends use and one you use at work. And these may change over time.
The proliferation of names is made even more maddening when other languages are added to the mix. How can you decide what is the "real" name? Let's look at one example.
Case of Johann Georg Schöndorf
I have discussed my Schoendorf line before (here and here). Records for this line are in French, German and Latin. Records for Johann Georg Schöndorf who lived in the 1700s are in both Latin and French. In his marriage record, a French record, he is "Jean George Schöndorf".
In his son's marriage record, a Latin record, he is listed as "Johannis Georgii Schöndorff".
There are two issues here. First, the name is in Latin and, second, the name has a special form because it is possessive. This form is in the genitive case. If we want to cite the Latin name, we should convert it to the nominative case, which is what is used as the default. In this case the name would be "Johannes Georgius Schöndorf". For more on Latin, check out this post.
But, I know he spoke German, so what do we do? Do we convert the name to German or not? It seems unlikely that he would use the Latin and French forms outside of records. Fortunately, we have examples of the German name in his signature on the same two documents.
In this case it is probably safe to use the German form, but what if the only records you have are in Latin and not the local language? Ultimately, you get to decide what name to use. The most important things to do are be consistent, so others will understand what you are doing, and recognize the reality that for some questions there is not always a clear or final answer. When you are transcribing a record, you should keep the name as close to what is found in the record and, to clarify, you can add a standardized name in brackets, such as "Jean George Schöndorf [Johann Georg Schöndorf]".