We're working on a translation for all English-speaking players, but this could - unfortunately - take a little while.
First question: How do I use "Weisheit der Altvorderen"?
The wisdom of ancients, how it is called in English, is the ability of the Rivendell-sages/scholars. Affect this spell on an unit which has a special ability and it gets unlocked for use.
Next question: The difference between "Waffenmeister, Bruchtal-Schwertkampfer and Bruchtal-Lanzentrager":
The Waffenmeister (swordmasters (?)) are the elite-units of the barracks or Rivendell at all, they are very strong in attack and defense.
The Schwertkämpfer are the standart-infantry of Rivendell, and the "Lanzenträger" are troops (infantry) with lances to fight any mounted unit. Very powerfull against horses and monsters like trolls, but less usefull to fight "normal" troops like marksmen.
Last but not least: How can I produce Gwaihir?
You have to buy all the upgrades in your fortress, then you can buy the so called "Adlerhorst". Then Gwaihir can be bought.
Sincerely, Elros.