locale: Implemented SDL_GetPreferredLocales().

This was something I proposed a long time ago, Sylvain Becker did
additional work on it, then back to me.

Fixes Bugzilla #2131.

include/SDL.h

@@ -59,6 +59,7 @@
 #include "SDL_timer.h"
 #include "SDL_version.h"
 #include "SDL_video.h"
+#include "SDL_locale.h"
 
 #include "begin_code.h"
 /* Set up for C function definitions, even when using C++ */

include/SDL_events.h

@@ -85,6 +85,8 @@ typedef enum
                                      Called on Android in onResume()
                                 */
 
+    SDL_LOCALECHANGED,  /**< The user's locale preferences have changed. */
+
     /* Display events */
     SDL_DISPLAYEVENT   = 0x150,  /**< Display state change */
 

include/SDL_hints.h

@@ -1348,6 +1348,21 @@ extern "C" {
 #define SDL_HINT_AUDIO_DEVICE_STREAM_NAME "SDL_AUDIO_DEVICE_STREAM_NAME"
 
 
+/**
+ *  \brief Override for SDL_GetPreferredLocales()
+ *
+ *  If set, this will be favored over anything the OS might report for the
+ *  user's preferred locales. Changing this hint at runtime will not generate
+ *  a SDL_LOCALECHANGED event (but if you can change the hint, you can push
+ *  your own event, if you want).
+ *
+ *  The format of this hint is a comma-separated list of language and locale,
+ *  combined with an underscore, as is a common format: "en_GB". Locale is
+ *  optional: "en". So you might have a list like this: "en_GB,jp,es_PT"
+ */
+#define SDL_HINT_PREFERRED_LOCALES "SDL_PREFERRED_LOCALES"
+
+
 /**
  *  \brief  An enumeration of hint priorities
  */

include/SDL_locale.h

@@ -0,0 +1,101 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+/**
+ *  \file SDL_locale.h
+ *
+ *  Include file for SDL locale services
+ */
+
+#ifndef _SDL_locale_h
+#define _SDL_locale_h
+
+#include "SDL_stdinc.h"
+#include "SDL_error.h"
+
+#include "begin_code.h"
+/* Set up for C function definitions, even when using C++ */
+#ifdef __cplusplus
+/* *INDENT-OFF* */
+extern "C" {
+/* *INDENT-ON* */
+#endif
+
+
+typedef struct SDL_Locale
+{
+    const char *language;  /**< A language name, like "en" for English. */
+    const char *country;  /**< A country, like "US" for America. Can be NULL. */
+} SDL_Locale;
+
+/**
+ *  \brief Report the user's preferred locale.
+ *
+ *  This returns an array of SDL_Locale structs, the final item zeroed out.
+ *  When the caller is done with this array, it should call SDL_free() on
+ *  the returned value; all the memory involved is allocated in a single
+ *  block, so a single SDL_free() will suffice.
+ *
+ *  Returned language strings are in the format xx, where 'xx' is an ISO-639
+ *  language specifier (such as "en" for English, "de" for German, etc).
+ *  Country strings are in the format YY, where "YY" is an ISO-3166 country
+ *  code (such as "US" for the United States, "CA" for Canada, etc). Country
+ *  might be NULL if there's no specific guidance on them (so you might get
+ *  { "en", "US" } for American English, but { "en", NULL } means "English
+ *  language, generically"). Language strings are never NULL, except to
+ *  terminate the array.
+ *
+ *  Please note that not all of these strings are 2 characters; some are
+ *  three or more.
+ *
+ *  The returned list of locales are in the order of the user's preference.
+ *  For example, a German citizen that is fluent in US English and knows
+ *  enough Japanese to navigate around Tokyo might have a list like:
+ *  { "de", "en_US", "jp", NULL }. Someone from England might prefer British
+ *  English (where "color" is spelled "colour", etc), but will settle for
+ *  anything like it: { "en_GB", "en", NULL }.
+ *
+ *  This function returns NULL on error, including when the platform does not
+ *  supply this information at all.
+ *
+ *  This might be a "slow" call that has to query the operating system. It's
+ *  best to ask for this once and save the results. However, this list can
+ *  change, usually because the user has changed a system preference outside
+ *  of your program; SDL will send an SDL_LOCALECHANGED event in this case,
+ *  if possible, and you can call this function again to get an updated copy
+ *  of preferred locales.
+ *
+ *   \return array of locales, terminated with a locale with a NULL language
+ *           field. Will return NULL on error.
+ */
+extern DECLSPEC SDL_Locale * SDLCALL SDL_GetPreferredLocales(void);
+
+/* Ends C function definitions when using C++ */
+#ifdef __cplusplus
+/* *INDENT-OFF* */
+}
+/* *INDENT-ON* */
+#endif
+#include "close_code.h"
+
+#endif /* _SDL_locale_h */
+
+/* vi: set ts=4 sw=4 expandtab: */