Having read many gothic forums weird posts over the years, i can certainly understand why Gothic players are unable to differentiate between continuous and progressive aspects of the spoken tenses which relate to time within a constructed sentence, past and present tenses can me mixed together the expression depending on the grammarian's intention. German is the only other language spoken with English tense progression.
When Piranha Bytes developers applied the dialogue into the gothic game, they were grammatically perfect with Saturas's spoken english dialogue and in fact there are no mistakes, why they should have ever agreed it was a mistake is beyond reason, maybe just to keep the fans happy.
After Xardas broke away from the twelve magicians to go his own way to follow the dark arts of death (necromancy) Milten was admitted into the firemages guild to make up the empty place on the pentagram tips in the fire-mages house, he was the thirteenth magician to be introduced in conjunction with the game story-line, this means that any progressing future dialogues referring to Xardas can have the past participle applied as Saturas's sentence construction rightfully shows.
In the early gothic chapters before our nameless hero meets with Xardas, in line with the evolving story-line, pc-hero is unaware of any thirteenth magician - but because Saturas says -->"be patient! (present tense) well when we" (the past tense) "the twelve magicians, created the barrier back then, our powers were directed and controlled by" - - (now at this very point the English/Germanic present tense progression kicks in) - - "a thirteenth magician" (the past participle) still relative and perfectly progressing referring to *after* Miltens inclusion.
Glad to see JDR13 sticking to his guns on this subject, most impressive, hope he wasn't too distracted.