Special:RedirectEntity can be tried for all entities (it is not specific to items)
However when testing with 2 lexeme IDs I get an odd error message specifying that they are not empty items.
The i18n message needs to be updated to switch from the word "item" to "entity"
GIVEN I am on Special:RedirectEntity
AND I try to merge two Lexemes
THEN I should get the error message "Error: Can't create redirect on non empty entity L1234."