This is a great work. (I am german and this is one of my fav weapons) In the middle ages only knights were allowed to own and to fight with a sword. So the langes Messer was the weapon of the "normal soldier". And because of "swords" were the weapons of the knights, they named this weapon langes Messer (long knife).
It's a pretty unclear subject since messer just means knife, but usually langes messer and krieg messer are interchangeable for the larger hand-and-a-half or two-handed saber-knives. The grosse messer or often just messer is usually regarded as the smaller types, usually for one hand. If you are familiar with the Cold Steel Grosse Messer, that is a bit of a misnomer.
Haven't really made any messers lately. Most of these older ones were made on custom order. Would like to add one for use with Durer or Talhoffer though in our current semi-production/semi-custom lineup.
Not quite. Messer is just knife in German, but the term messer nowadays applies specifically to large war knives that usually had the slab handles and a nagel for hand protection. There were lots of manuals written for messer dueling/combat. A falchion, on the other hand, was often more a footman's weapon. Similar shape but not really made or used the same.
Langes translates to long, so langes messer and grosse messer are commonly used to describe the longer, larger messers, usually hand and a half or two handed. Messer could refer to either that particular type of weapon/tool or the one-handed smaller brethren.