Another example: it is a difference whether you make Locher (punchers) or Löcher (holes).
Or "Räucherlachs" (smoked salmon) and "Raucherlachs" (does not really exist - "salmon for smokers")
A "Kämpfer" is a fighter, but "Kampfer" is camphor.
"schön": beautiful, "schon": "already".
"Vater": father, "Väter": fathers
"Lösung": solution, "Losung": slogan / droppings
Or if you do a double replacement of "sehr mäßig" (very moderate) and you replace the "ä" with "a" and the "ß" with "ss" it becomes "sehr massig" (very massive/huge).
If the whole exercise is about getting a filename without accents etc. then I would suggest that only the filename gets the treatment in Convert>Tag-Filename and the
Format string: $replace(%track% - %title%,á,a,é,e,í,i,ó,o,ú,u,Á,A,É,E,Í,I,Ó,O,Ú,U,ü,u,Ü,U,ñ,n,Ñ,N,è,e,ê,e,ì,i,î,i,ï,i,à,a,â,a,ò,o,ô,o,ù,u,û,u,ç,c,Ç,C,ß,ss,œ,oe,Œ,OE)
(expand the field list to the mask that you usually use to create filenames).
That preserves the original data in the tag fields and help with the filenames.
On a footnote: $replace() allows up to 32 pairs. The current expression has far more. It would have to be split.