Add sdl3_locale.odin

vendor/sdl3/sdl3_locale.odin

@@ -0,0 +1,13 @@
+package sdl3
+
+import "core:c"
+
+Locale :: struct {
+	language: cstring,  /**< A language name, like "en" for English. */
+	country:  cstring,  /**< A country, like "US" for America. Can be NULL. */
+}
+
+@(default_calling_convention="c", link_prefix="SDL_", require_results)
+foreign lib {
+	GetPreferredLocales :: proc(count: ^c.int) -> [^]^Locale ---
+}