PsychoPy 2026.2.3/2026.2.4 cannot launch on macOS 27

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Hi everyone,

I am experiencing a launch error with PsychoPy Standalone on a new Apple Silicon Mac, and I would appreciate any help identifying the cause.

System:

  • MacBook Air with Apple M5
  • macOS 27
  • System locale: zh_CN.UTF-8

PsychoPy versions tested:

  • PsychoPy 2026.2.3 macOS arm64, Python 3.10
  • PsychoPy 2026.2.3 macOS arm64, Python 3.11
  • PsychoPy 2026.2.4 macOS arm64, Python 3.10
  • PsychoPy 2026.2.4 macOS arm64, Python 3.11

All four builds fail immediately at launch with the same type of py2app “Launch error”.

I have already tried the following:

  1. Removed PsychoPy and reinstalled it.

  2. Used AppCleaner to remove PsychoPy and related files, then performed a clean reinstall.

  3. Renamed the existing .psychopy3 folder so PsychoPy would create a completely fresh configuration directory.

  4. Renamed/recreated userPrefs.cfg and appData.cfg.

  5. Changed macOS preferred languages to English only.

  6. Tried launching PsychoPy directly from Terminal with an English locale:

    env LANG=en_US.UTF-8 LC_ALL=en_US.UTF-8 /Applications/PsychoPy.app/Contents/MacOS/PsychoPy

None of these solved the problem.

My current Terminal locale is:

LANG=“zh_CN.UTF-8”
LC_COLLATE=“zh_CN.UTF-8”
LC_CTYPE=“zh_CN.UTF-8”
LC_MESSAGES=“zh_CN.UTF-8”
LC_MONETARY=“zh_CN.UTF-8”
LC_NUMERIC=“zh_CN.UTF-8”
LC_TIME=“zh_CN.UTF-8”
LC_ALL=

With a fresh .psychopy3 directory, PsychoPy crashes before userPrefs.cfg or appData.cfg are even created.

For PsychoPy 2026.2.4 macOS arm64 with Python 3.10, the current last_app_load.log is:

Traceback (most recent call last):
File “/Applications/PsychoPy.app/Contents/Resources/boot.py”, line 262, in
_run()
File “/Applications/PsychoPy.app/Contents/Resources/boot.py”, line 185, in _run
exec(compile(source, path, “exec”), globals(), globals())
File “/Applications/PsychoPy.app/Contents/Resources/psychopyApp.py”, line 207, in
main()
File “/Applications/PsychoPy.app/Contents/Resources/psychopyApp.py”, line 196, in main
_ = startApp(
File “/Applications/PsychoPy.app/Contents/Resources/lib/python3.10/psychopy_app/init.py”, line 130, in startApp
_psychopyAppInstance = PsychoPyApp(
File “/Applications/PsychoPy.app/Contents/Resources/lib/python3.10/psychopy_app/_psychopyApp.py”, line 256, in init
if not wx.Locale.IsAvailable(locale):
wx._core.wxAssertionError: C++ assertion “lang == wxLANGUAGE_DEFAULT” failed at /private/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/cibw-sdist-6srn_ms4/wxpython-4.2.5/ext/wxWidgets/src/common/intl.cpp(781) in IsAvailable(): No info for a valid language?

The Python 3.11 build of PsychoPy 2026.2.4 fails at the same wx.Locale.IsAvailable(locale) call.

PsychoPy 2026.2.3 also produced essentially the same error with both Python 3.10 and 3.11.

Since the error persists across:

  • two PsychoPy versions,
  • both Python 3.10 and 3.11 builds,
  • a completely fresh .psychopy3 directory,
  • English-only macOS preferred languages,
  • and an explicitly forced en_US.UTF-8 environment,

I am wondering whether this may be a compatibility issue between PsychoPy Standalone / wxPython / wxWidgets and macOS 27.

Has anyone reproduced this on macOS 27, or is there another workaround I could try?

Thank you very much!