If both are used in canon, I'm sure they're both valid. Neither seems to be used as an actual German surname, as far as I can tell, but Lehnsherr is at least an actual German word (meaning 'liege'). I think I favour Lehnsherr, although Lensherr is the spelling used in this particular film.
(His first name has also been rendered as both Erik and Eric by canonical sources, but Erik seems to be generally agreed upon there. Blast, I thought I wouldn't have problems like this again after Jeremy O/Usbo(u)rne of Peep Show.)
On a less frustrating note, yes, James McAvoy's accent is magnificent.
(EDIT: OH, OH, ALSO: if you haven't heard McAvoy's natural accent before, I can only assume you haven't seen this clip, which is utterly, utterly charming and delightful. You don't have to watch it if you don't want to, but there it is. It involves singing, although most of it is done by Michael Fassbender because McAvoy is rubbish and doesn't know any of the words.)
Re: I have no Marvel icons ): I shall have to make do with Wondy instead
(His first name has also been rendered as both Erik and Eric by canonical sources, but Erik seems to be generally agreed upon there. Blast, I thought I wouldn't have problems like this again after Jeremy O/Usbo(u)rne of Peep Show.)
On a less frustrating note, yes, James McAvoy's accent is magnificent.
(EDIT: OH, OH, ALSO: if you haven't heard McAvoy's natural accent before, I can only assume you haven't seen this clip, which is utterly, utterly charming and delightful. You don't have to watch it if you don't want to, but there it is. It involves singing, although most of it is done by Michael Fassbender because McAvoy is rubbish and doesn't know any of the words.)