A gunsmith good enough to be entrusted with a Lang should probably be expensive.
The single triggers used in Spanish guns are considered to be unreliable. That is because they are direct copies of the single triggers used in English guns. If it is your lucky day, perhaps the gunsmith will find some dirt or hardened lube in a place that impedes the workings of said trigger. But, often, that is not the case. Inertia single trigger designs often need a good thump of recoil to make them consistently operational, and we tend to load these old guns with the lightest recoiling and lowest pressure loads we can find. My father, RIP, put big, squishy recoil pads on everything he ever owned, and the pad he had put on a Beretta he owned impeded the inertia single trigger on the gun. It became reliable again after time hardened the pad up. My Dad quit using the gun when the trouble he had unknowingly caused, started. Took 20 years or so of sitting around for it to get better.
Hopefully, it is something easy to diagnose and rectify.
Good luck.
Best,
Ted
