Quite weird. It's not in the 1st edition of the OED. It might be a mispelling, but I see it accounts for 3 translations in the LEO dictionary: Ach je, O je, and O Herr. At first I thought it might be a Scots interjection for "Lord!" but don't quote me. It is not an Old English word. Who knows?
Thanks for bringing something to us from OEDILF. If jheem doesn't know, I don't have a lot of hope of finding out! However, I will take it to my logophile friend to see if he can help. Would aput maybe know something about it?
The rendering 'O Herr' certainly suggests it's just a spelling variant of 'lor'. I don't know what the nuances of 'ach je' and 'O je' are, but perhaps in German 'O Herr' is stronger, and the other two are closer to the normal English use of 'oh lor'.
I wonder if the spelling <oer> is meant to represent the pronunciation [oə]. The old OED gives the pronunciations [lO:d] for 'lord' but [loə] for 'lore', so it's possible that clipping the [d] changed the vowel for some speakers (but OED show [lO:] for 'lor'). This distinction in vowels is no longer made -- 'lore' and 'lord' now have the same vowel.
Except in Scottish, where Chambers shows 'lord' as [lOrd] and 'lore' as [lor] or [lOr]. They list but don't transcribe 'lor'.
So that's all I can think of -- it's the ordinary exclamation 'lor', but with the vowel of 'lore', in some accent where the two vowels were different.
As to that, I'd guess they got it from some writer who used 'dialect' -- someone like Scott, perhaps; and given a translation of a work of his into German, thought this was a bona fide English word.
