tdf#91288 Does not display traditional Chinese variant of

Noto fonts correctly.

LanguageTag()::getLanguage() would always return "zh" despite
traditional Chinese were choose. hb_language_from_string()
requires iso639-3 language tag except for Chinese, so
we use use Bcp47() language tag for Chinese to differ zh-CN and
the others.

Change-Id: I6700a79a9c49a97d840b430def77741912935f72
Reviewed-on: https://gerrit.libreoffice.org/20027Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit 4424daa2)
Reviewed-on: https://gerrit.libreoffice.org/20204
(cherry picked from commit 48cf2d9f)

vcl/generic/glyphs/gcach_layout.cxx

@@ -461,8 +461,10 @@ bool HbLayoutEngine::Layout(ServerFontLayout& rLayout, ImplLayoutArgs& rArgs)
             int nEndRunPos = it->mnEnd;
             int nRunLen = nEndRunPos - nMinRunPos;
             maHbScript = it->maScript;
+            // hb_language_from_string() accept ISO639-3 language tag except for Chinese.
+            LanguageTag &rTag = rArgs.maLanguageTag;
+            OString sLanguage = OUStringToOString( MsLangId::isChinese(rTag.getLanguageType()) ? rTag.getBcp47():rTag.getLanguage() , RTL_TEXTENCODING_UTF8 );
 
-            OString sLanguage = OUStringToOString(rArgs.maLanguageTag.getLanguage(), RTL_TEXTENCODING_UTF8);
 
             static hb_unicode_funcs_t* pHbUnicodeFuncs = getUnicodeFuncs();