Some subject searches to try in SOLO:
Law Germany History
Law Germany Sources
Law, Saxon
Law, Germanic
Feudal Law - Germany
Land tenure -- Law and legislation -- Germany -- Early works to 1800
Feudalism - Germany
Civil law - Germany - History
Some digital libraries of older texts
Lehnrecht (feudal law)
Herr (lord)
Mann, Vasall
Treue
Hulde, Huldigung
Kommendation (act of fealty)
Grundherrschaft (manorialism)
Schöffen (law-finders)
Sachsenspiegel (mirror of the Saxons) Eike von Repgow
Deutschenspiegel
Schwabenspiegel (mirror of the Swabians)
Steiermärkisches Landrechtsbuch, Styrian Law Book
Wiener Stadtrechtsbuch, Vienna City Law Book
Weistüm
Systematische Schoffenrecht
"The reception of Roman law in Germany: an interpretation" by W.Kunkel is in Pre-reformation Germany ed Strauss (1972) which can be ordered from Closed Stacks
Handwörterbuch zur Deutsche Rechtsgeschichte complete 1st ed Taylorian REF.G.25.
Handwörterbuch zur Deutsche Rechtsgeschichte 2nd ed Bodleian URR.Ref.368
The yet to be completed
Deutsches Rechtswörterbuch : Wörterbuch der älteren deutschen Rechtssprache is in the Law Bod at German 450 D486
and is freely available online see link below