Here is a Google Translation of the German, whihc is always a little cryptic. :-):
"sa adzes , type catalog 1986, p 134 ; Klesse , glass catalog of Cologne; Examples in most publications on medieval glass and for early 1900"
The translation of that text appears to reference a catalog of medieval glass and it says early 1900, which I am going to assume is a translation for early 1900's.
The mark commonly found on these precludes a 1900 time frame. This production is pretty firmly ca 1925-35. Some may call that early 1900's.
Possibly a German / English speaking member can translate the phrase more concisely.