I'm not sure if you still want this or not. Here, fwiw, is output of your use Devel::Peek

1 of 2 Here comes $s, the contents of cell at row 636, column 2 of fil
+e .../BirdLists_in_english/AERC WPlist July 2010 version 2.0.ods
$s = Güldenstädt’s Redstart


SV = PV(0x201601c) at 0x2020ca0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK,UTF8)
  PV = 0x468ffe4 "G\303\274ldenst\303\244dt\342\200\231s Redstart"\0 [
+UTF8 "G\x{fc}ldenst\x{e4}dt\x{2019}s Redstart"]
  CUR = 26
  LEN = 27
SV = PVMG(0x460a77c) at 0x2020ca0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x45ff86c "G\303\274ldenst\303\244dt\342\200\231s Redstart"\0 [
+UTF8 "G\x{fc}ldenst\x{e4}dt\x{2019}s Redstart"]
  CUR = 26
  LEN = 175
  MAGIC = 0x418ce64
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 22





2 of 2 Here comes $s, the contents of cell at row 763, column 8 of fil
+e .../BirdLists_in_both_languages/53174_Liste_Pal_OccO2008.ods
$s = Güldenstädt's Redstart
SV = PVMG(0x460a77c) at 0x2020ca0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK,UTF8)
  IV = 0
  NV = 0
  PV = 0x27bd014 "G\303\274ldenst\303\244dt's Redstart"\0 [UTF8 "G\x{f
+c}ldenst\x{e4}dt's Redstart"]
  CUR = 24
  LEN = 779
  MAGIC = 0x280913c
    MG_VIRTUAL = &PL_vtbl_utf8
    MG_TYPE = PERL_MAGIC_utf8(w)
    MG_LEN = 22
[download]

RichardH
Update
Summary
Here are the summarized results of
"use Devel::Peek;"

WITH:- use open ':std', ':encoding(cp1252)';
File AERC*.ods :-
PV = 0x34b5cf4 "G\303\274ldenst\303\244dt's Redstart"\0 [UTF8 "G\x{fc}ldenst\x{e4}dt's Redstart"]

File Pal_*.ods :-
PV = 0x34b5cf4 "G\303\274ldenst\303\244dt's Redstart"\0 [UTF8 "G\x{fc}ldenst\x{e4}dt's Redstart"]

WITHOUT:-
File AERC*.ods :-
PV = 0x45fc33c "G\303\274ldenst\303\244dt\342\200\231s Redstart"\0 [UTF8 "G\x{fc}ldenst\x{e4}dt\x{2019}s Redstart"]

File Pal_*.ods :-
PV = 0x4660024 "G\303\274ldenst\303\244dt's Redstart"\0 [UTF8 "G\x{fc}ldenst\x{e4}dt's Redstart"]

Conclusion
To remove differences between OOorg codings
include the line
"use open ':std', ':encoding(cp1252)';"