Enable UTF-8 mode by default (implement PEP 686)

[AA-Turner]

Feature or enhancement

Proposal:

See PEP 686

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

PEP 686, approved for Python 3.15.

Linked PRs

• GH-133711: Enable UTF-8 mode by default (PEP 686) #133712
• gh-133711: Fix test_regrtest for PYTHONUTF8=1 #134839
• gh-133711: Log Windows OEM code page in test.pythoninfo #134840
• gh-133711: Fix test_readline.test_nonascii() for UTF-8 Mode #134841
• [3.14] gh-133711: Fix test_regrtest for PYTHONUTF8=1 (GH-134839) #134842
• [3.13] gh-133711: Fix test_regrtest for PYTHONUTF8=1 (GH-134839) #134843
• [3.14] gh-133711: Fix test_readline.test_nonascii() for UTF-8 Mode (GH-134841) #134851
• [3.13] gh-133711: Fix test_readline.test_nonascii() for UTF-8 Mode (GH-134841) #134852

[serhiy-storchaka]

Please wait until we fix all errors in the tests and the stdlib when running in a non-UTF-8 locale (see #133677). Then ensure that all tests are still passed in a non-UTF-8 locale after this change.