Replace wxLocaleIdent ctor from language with FromTag()

This static function parses a subset of the language tags described in
BCP 47 (see https://www.rfc-editor.org/rfc/bcp/bcp47.txt).

Use the tag, as specified by this function, rather than the locale
identifiers components under MSW, where this should allow us to use even
locales that can't be described using just language-script-region.

include/wx/uilocale.h

@@ -33,17 +33,14 @@ enum
 class WXDLLIMPEXP_BASE wxLocaleIdent
 {
 public:
+    // Create the object from BCP 47-like language tag: the string must contain
+    // at least the language part (2 or 3 ASCII letters) and may contain script
+    // and region separated by dashes.
+    static wxLocaleIdent FromTag(const wxString& tag);
+
     // Default ctor creates an empty, invalid identifier.
     wxLocaleIdent() { }
 
-    // Construct from language, i.e. a two-letter ISO 639-1 code (or a
-    // three-letter ISO 639-2 code if there is no ISO 639-1 code for this
-    // language).
-    wxLocaleIdent(const char* language)
-        : m_language(wxString::FromAscii(language))
-    {
-    }
-
     // Set language
     wxLocaleIdent& Language(const wxString& language);
 
@@ -69,6 +66,11 @@ public:
     // Construct platform dependent name
     wxString GetName() const;
 
+    // Get the language tag: for the objects created with FromTag() returns the
+    // string passed to it directly, otherwise reconstructs this string from
+    // the components.
+    wxString GetTag() const;
+
     // Empty locale identifier is invalid. at least Language() must be called.
     bool IsEmpty() const
     {
@@ -76,6 +78,8 @@ public:
     }
 
 private:
+    wxString m_tag;
+
     wxString m_language;
     wxString m_region;
     wxString m_script;