macOS: Set LANG to en_US if cocoa reports language as en_* that is not a valid locale

Fixes #3899

kitty/cocoa_window.m

@@ -574,12 +574,7 @@ cocoa_get_lang(PyObject UNUSED *self) {
         locale = [[NSLocale currentLocale] localeIdentifier];
     }
     if (!locale) { Py_RETURN_NONE; }
-    // Make sure the locale value is valid, that is it can be used
-    // to construct an actual locale
     const char* locale_utf8 = [locale UTF8String];
-    locale_t test_locale = newlocale(LC_ALL_MASK, locale_utf8, NULL);
-    if (!test_locale) { Py_RETURN_NONE; }
-    freelocale(test_locale);
     return Py_BuildValue("s", locale_utf8);
 
     } // autoreleasepool

kitty/data-types.c

@@ -23,6 +23,7 @@
 #include <signal.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <locale.h>
 #ifdef WITH_PROFILER
 #include <gperftools/profiler.h>
 #endif
@@ -156,6 +157,15 @@ wcwidth_wrap(PyObject UNUSED *self, PyObject *chr) {
     return PyLong_FromLong(wcwidth_std(PyLong_AsLong(chr)));
 }
 
+static PyObject*
+locale_is_valid(PyObject *self UNUSED, PyObject *args) {
+    char *name;
+    if (!PyArg_ParseTuple(args, "s", &name)) return NULL;
+    locale_t test_locale = newlocale(LC_ALL_MASK, name, NULL);
+    if (!test_locale) { Py_RETURN_FALSE; }
+    freelocale(test_locale);
+    Py_RETURN_TRUE;
+}
 
 static PyMethodDef module_methods[] = {
     {"wcwidth", (PyCFunction)wcwidth_wrap, METH_O, ""},
@@ -169,6 +179,7 @@ static PyMethodDef module_methods[] = {
     {"parse_bytes", (PyCFunction)parse_bytes, METH_VARARGS, ""},
     {"parse_bytes_dump", (PyCFunction)parse_bytes_dump, METH_VARARGS, ""},
     {"redirect_std_streams", (PyCFunction)redirect_std_streams, METH_VARARGS, ""},
+    {"locale_is_valid", (PyCFunction)locale_is_valid, METH_VARARGS, ""},
 #ifdef __APPLE__
     METHODB(user_cache_dir, METH_NOARGS),
     METHODB(process_group_map, METH_NOARGS),

kitty/fast_data_types.pyi

@@ -672,6 +672,10 @@ def cocoa_get_lang() -> Optional[str]:
     pass
 
 
+def locale_is_valid(name: str) -> bool:
+    pass
+
+
 def mark_os_window_for_close(os_window_id: int, cr_type: int = 2) -> bool:
     pass
 

kitty/main.py

@@ -195,10 +195,15 @@ run_app = AppRunner()
 def ensure_macos_locale() -> None:
     # Ensure the LANG env var is set. See
     # https://github.com/kovidgoyal/kitty/issues/90
-    from .fast_data_types import cocoa_get_lang
+    from .fast_data_types import cocoa_get_lang, locale_is_valid
     if 'LANG' not in os.environ:
         lang = cocoa_get_lang()
         if lang is not None:
+            if not locale_is_valid(lang):
+                if lang.startswith('en_'):
+                    lang = 'en_US'
+                else:
+                    log_error(f'Could not set LANG Cocoa returns language as: {lang}')
             os.environ['LANG'] = lang + '.UTF-8'