intl: configure default locale

[bnoordhuis]

Right now Node.js (by omission) leaves it up to ICU to figure out the locale and configure itself accordingly.

That's problematic for a number of reasons, see e.g. #27856 (comment) - tl;dr environment variables affect the output of Date#toString(). Googling for variations of 'nodejs lc_all' suggests the issue pops up more often.

Since one of Node.js's goals is to provide a consistent experience across platforms and environments, I think it would be good to explicitly configure the locale at startup instead of leaving it to happenstance.

There are two ways to accomplish that and they're not mutually exclusive:

1. setenv("LC_ALL", "..."); setenv("LC_MESSAGES", "..."); // etc.
2. icu::Locale::setDefault(...)

I'm adding the semver-major label because there is some risk of breaking existing applications. (Libraries not so much since the average library already runs in a variety of environments.)

It would be good to have some discussion on the merits of both (and alternative?) approaches.

[sam-github]

@nodejs/intl

[silverwind]

Agree, things like Date#toString output must be stable. The variants that support locale like Date#toLocale​String should of course factor in locale settings.

[silverwind]

Would setenv affect other libraries like V8? If so, the icu APIs are probably safer to use.

[bnoordhuis]

Other libraries: yes. V8: probably not since it uses ICU.

The "other libraries" part is arguably a pre because you want different parts of Node.js to agree on the locale.

FWIW, the ICU-only patch for people who want to try it:

diff --git a/src/node.cc b/src/node.cc
index e168d62c51..08826678bb 100644
--- a/src/node.cc
+++ b/src/node.cc
@@ -93,6 +93,7 @@
 #include <sys/types.h>
 
 #if defined(NODE_HAVE_I18N_SUPPORT)
+#include <unicode/locid.h>
 #include <unicode/uvernum.h>
 #endif
 
@@ -883,6 +884,13 @@ InitializationResult InitializeOncePerProcess(int argc, char** argv) {
   // Hack around with the argv pointer. Used for process.title = "blah".
   argv = uv_setup_args(argc, argv);
 
+#ifdef NODE_HAVE_I18N_SUPPORT
+  {
+    UErrorCode status = U_ZERO_ERROR;
+    icu::Locale::setDefault(icu::Locale::getUS(), status);
+  }
+#endif  // NODE_HAVE_I18N_SUPPORT
+
   InitializationResult result;
   result.args = std::vector<std::string>(argv, argv + argc);
   std::vector<std::string> errors;

(The US-centricity makes it kind of blergh but one thing at a time.)

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