Remove, mark "rare" (or perhaps regional?), or add new meanings:
This is one of those words that is 'unidirectional' in a way; worth keeping in the dictionary from E -> D in case anyone runs across this word in English, but as a D -> E translation of 'dummkopf' this would be a poor choice indeed, unless you're living in the 16th century (but see below).
In the singular, this most often means a kind of turtle. If the entry is kept and not deleted, the turtle meaning should certainly be added.
The plural form in the common expression 'to be at loggerheads with s.o.' comes from the uncommon word 'loggerhead', which is a metal tool ending in a ball used for heating. This is not a word I ever encountered before searching for it, so perhaps it is also rare or obsolete. If the entry is kept, this meaning should be added.
The slangy 'dummkopf' meaning of 'loggerhead' is supported by a 1588 citation in M-W, but I never heard the English term used this way. Perhaps it is regional (UK or elsewhere?)--need some Brits et al. to weigh in on this so we know whether to eliminate this meaning or mark it regional.
There should probably also be a link to the '...loggerheads...' search, which turns up five translations, currently.