The unclued lights (ignore two apostrophes and an umlaut) are of a kind, as verified in Brewer.
 

Across

1    Seating right up to date (5, two words)
6    Run off book in a moment, not English (7)
11    Learner chews roach sadly (10, hyphened)
15    Shortly irritate returning US politician (4)
16    Bill interprets old fears (7)
17    One or two stones from Orkney twirled in hat (7)
18    Menial Japanese character (3)
19    In tense state, less experienced, he spins out at length (10)
21    Holy book is first, in this (5)
27    Almost left (4)
28    As wood, stingy type takes chestnut (5)
30    Operation is free but lots pay (10)
35    Duke’s place...