There is nothing German about that gun... the lock is English. The Golcher family were lock makers in Wednesbury, Staffordshire. At least one of them emigrated to the US and may have made or assembled or finished locks here. The gun itself is American, a very late flintlock, perhaps 1820-30. It isn't German script, its a stylized "old English."
Also, if anyone needs help, I have Stockel, both the "new" version and the original in Danish. (I bought Merrill Lindsay's copies at the sale of his collection.) It isn't all its cracked up to be. The quality of the new version is spotty and depends on the sources used. The additions aren't original research but are taken from other published lists so it copies the mistakes along with the good information. I suspect the material on European makers is better. Stockel was a Danish Army officer. I think the first volume was published in 1938 and the 2nd in 1942 so, at best, his research tools were limited. Eugene Heere updated it in the 70s by adding the collected material of all the published lists to that date. In my own area of expertise, I give Heere credit for taking a very conservative approach and not including some of the wilder claims. It's the first source I've seen that has Thomas Ketland Sr's correct date of birth although the citation is simply the completely useless "archives of the country". I have found the archival source, but I wish I knew where Heere got the date.
Its 3 or 4 volumes... if that ad is asking $800 for two, its only half of the set! The original version is in 2 volumes. It is in Danish and is very rare. The ones I have are the only ones I've ever seen and that might justify such a high price if someone really wanted them.