Bug manifests on Windows 10 ( I haven't tested other versions). Before
starting emacs:

C:\Users\JoakimHårsman>chdir
C:\Users\JoakimHårsman

C:\Users\JoakimHårsman>echo %HOME%
C:\users\JoakimHårsman

C:\Users\JoakimHårsman> runemacs -Q

Notice that the current directory which is the same as the HOME
environment, contains the letter å. After starting emacs with runemacs
-Q:

(expand-file-name default-directory)

returns

"c:/users/JoakimH  rsman/"

or alternatively

"c:/users/JoakimH\303\245rsman/"

while the correct return value should be

"c:/users/JoakimHårsman/"


In GNU Emacs 28.0.50 (build 1, x86_64-w64-mingw32)
Repository revision: 7640f1da0be206a7598c96acdfdaaf390a2b546c
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 10.0.19043
System Description: Microsoft Windows 10 Pro (v10.0.2009.19043.1165)

Configured using:
 'configure --prefix=/d/a/emacs-build/emacs-build/pkg/master-x86_64
 --with-native-compilation --with-zlib --with-gnutls --with-xml2
 --with-lcms2 --with-json --with-harfbuzz --without-cairo --with-rsvg
 --with-png --with-gif --without-tiff --with-jpeg --with-xpm
 --disable-build-details --disable-silent-rules --without-dbus
 --without-compress-install'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NATIVE_COMP
NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND THREADS TOOLKIT_SCROLL_BARS XPM
ZLIB

Important settings:
  value of $LANG: en_US.UTF8
  locale-coding-system: cp1252

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs auth-source eieio eieio-core eieio-loaddefs
password-cache json map text-property-search time-date mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail comp comp-cstr warnings subr-x rx cl-seq cl-macs cl-extra
help-mode seq byte-opt gv cl-loaddefs cl-lib bytecomp byte-compile cconv
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils iso-transl
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win w32-vars
term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice button
loaddefs faces cus-face macroexp files window text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads w32notify w32 lcms2 multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 89375 14408)
 (symbols 48 7898 1)
 (strings 32 22918 3463)
 (string-bytes 1 759569)
 (vectors 16 23743)
 (vector-slots 8 1091049 147200)
 (floats 8 29 266)
 (intervals 56 257 0)
 (buffers 992 12))