Use LC_TIME locale for strftime format string translations

We commonly mark strftime format strings for translation to account
for date/time representations without an existing strftime shortcut
("Yesterday %H%p"). As those translations are looked up according to
the locale defined by LC_MESSAGES, while the conversion characters
themselves are resolved according to LC_TIME, the result can be
rather odd when mixing locales ("Den 27. January"). The correct
solution would be to install translations for format strings in
the LC_TIME catalogue and look them up with dcgettext(), but we
don't have the infrastructure to do that easily. Work around this
by adding a helper method that looks up a string in LC_MESSAGES
using the locale defined by LC_TIME and use that to translate
format strings, which has the same result.

https://bugzilla.gnome.org/show_bug.cgi?id=738640

src/shell-util.c

@@ -12,6 +12,7 @@
 #include <gdk/gdkx.h>
 #include <X11/extensions/XTest.h>
 
+#include <locale.h>
 #ifdef HAVE__NL_TIME_FIRST_WEEKDAY
 #include <langinfo.h>
 #endif
@@ -208,6 +209,32 @@ shell_util_get_week_start ()
   return week_start;
 }
 
+/**
+ * shell_util_translate_time_string:
+ * @str: String to translate
+ *
+ * Translate @str according to the locale defined by LC_TIME; unlike
+ * dcgettext(), the translations is still taken from the LC_MESSAGES
+ * catalogue and not the LC_TIME one.
+ *
+ * Returns: the translated string
+ */
+const char *
+shell_util_translate_time_string (const char *str)
+{
+  const char *locale = g_getenv ("LC_TIME");
+  const char *res;
+
+  if (locale)
+    setlocale (LC_MESSAGES, locale);
+
+  res = gettext (str);
+
+  setlocale (LC_MESSAGES, "");
+
+  return res;
+}
+
 /**
  * shell_write_string_to_stream:
  * @stream: a #GOutputStream

src/shell-util.h

@@ -21,6 +21,7 @@ int      shell_util_get_week_start             (void);
 
 char    *shell_util_format_date                (const char       *format,
                                                 gint64            time_ms);
+const char *shell_util_translate_time_string   (const char *str);
 
 gboolean shell_write_string_to_stream          (GOutputStream    *stream,
                                                 const char       *str,