Don't look for catalogs in AddCatalogLookupPathPrefix() path directly.

Previously, the prefix directory itself for searched for catalogs, in
addition to prefix/lang/LC_MESSAGES and prefix/lang.  This never made
much sense, because only one catalog could be in such place, instead of
multiple catalogs for more languages.  It also prevented successful
identification of catalog's language and didn't work with
GetAvailableLanguages().

Remove this misfeature and update the documentation accordingly.  Update
OS X-specific code so that it continues to work (it previously depended
on this behavior).  As a side effect, *.lproj directories are now
recognized in all search prefixes, not just in Resources.

See #12498, #15253.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74441 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/translation.h

@@ -338,9 +338,10 @@ public:
     wxTranslations::SetLoader().
 
     Catalogs are searched for in standard places (system locales directory,
-    `LC_PATH` on Unix systems, Resources folder on OS X, executable's directory
-    on Windows), but you may also prepend additional directories to the search
-    path with AddCatalogLookupPathPrefix().
+    `LC_PATH` on Unix systems, Resources subdirectory of the application bundle
+    on OS X, executable's directory on Windows), but you may also prepend
+    additional directories to the search path with
+    AddCatalogLookupPathPrefix().
 
     @since 2.9.1
  */
@@ -349,7 +350,7 @@ class wxFileTranslationsLoader : public wxTranslationsLoader
 public:
     /**
         Add a prefix to the catalog lookup path: the message catalog files will
-        be looked up under prefix/lang/LC_MESSAGES, prefix/lang and prefix
+        be looked up under prefix/lang/LC_MESSAGES and prefix/lang directories
         (in this order).
 
         This only applies to subsequent invocations of