Really?, wow!
So the devs took their creative liberties:
Well, as I like to take screenshots, to admire the beautiful art of some cities I build, I also take screenshots of units to see what weapons they use after certain technologies, here are some curiosities, the weapon used by the janissaries in “Spanish”.
Well, in English it is “trench gun”. Look in various sources, and as you mentioned the Ottomans in the middle ages still used arquebuses and muskets. There is a mention on wikipedia that they used a “trench gun”. I checked the source, and I saw that it was an Osprey book, by David Nicolle, “Jenissaries” 1995.
I got screenshots of excerpts from the book, and found this on page 21:
In other words, that trench gun was a weapon from the 18th! 18th century! What an anachronism. The downside is that even though it’s an 18th century weapon, it’s not as powerful as it should be, at least also against melee infantry (that’s why I suggested increasing a bonus vs melee infantry).
Well anyway, it’s not like the book weapon were a real trench gun (as the original Winchester Model 1897 aka:Trench-Gun), it’s the name given to it by those who made the book because of its resemblance to one (the put the name in beetwen quotation marks). In theory the Ottoman arquebuses and muskets were different from the Western European arquebuses. I suppose that since it is not a traditional arquebus and less a hand cannon, they gave it that name in Spanish.
Here is another capture from the same book, pages 21 and 22 where he explains the evolution of the Janissary weaponry. As far as ranged weapons go, it looks like they skipped the “hand cannon” step, and went straight from the Bow to the matchlook Arquebus. As a peculiarity, their barrels were longer than Western arquebuses and had heavier bullets (20-80 grams).
