tests: fix locale used to execute tests

ChangeLog.asciidoc

@@ -73,6 +73,7 @@ https://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 * relay: display the arrow before client id and protocol in raw buffer
 * ruby: fix load of scripts requiring "uri" (issue #433)
 * ruby: fix Ruby detection when pkg-config is not installed
+* tests: fix locale used to execute tests
 
 [[1.3]]
 == Version 1.3 (2015-08-16)

tests/tests.cpp

@@ -125,7 +125,7 @@ main (int argc, char *argv[])
     char *weechat_tests_args, *args, **weechat_argv;
 
     /* setup environment: default language, no specific timezone */
-    setenv ("LANG", "C", 1);
+    setenv ("LC_ALL", "C", 1);
     setenv ("TZ", "", 1);
 
     /* build arguments for WeeChat */