Perhaps you have merged cells? Avoid selecting anyway:
Code:
with Columns("F:H")
.Replace What:="Dec", Replacement:="Dez", LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=True
.Replace What:="Oct", Replacement:="Okt", LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=True
.Replace What:="May", Replacement:="Mai", LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=True
.Replace What:="Mar", Replacement:="Mär", LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=True
.Replace What:="-", Replacement:=".", LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=True
End With