Introduce LanguageTagIcu::getDisplayName()

To be used in generating display names for on-the-fly language
tags in the language listbox.

Change-Id: Ibb36fe312e550f77f1e2d3acc2dbff9e83c15f7b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/120797
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins

1 files changed, 22 insertions, 0 deletions

diff --git a/i18nlangtag/source/languagetag/languagetagicu.cxx b/i18nlangtag/source/languagetag/languagetagicu.cxx
index c35e7a85ef8b..fd1c9bc75670 100644
--- a/i18nlangtag/source/languagetag/languagetagicu.cxx
+++ b/i18nlangtag/source/languagetag/languagetagicu.cxx
@@ -46,4 +46,26 @@ icu::Locale LanguageTagIcu::getIcuLocale( const LanguageTag & rLanguageTag, std:
            );
 }
 
+// static
+OUString LanguageTagIcu::getDisplayName( const LanguageTag & rLanguageTag, const LanguageTag & rDisplayLanguage )
+{
+    // This will be initialized by the first call; as the UI language doesn't
+    // change the tag mostly stays the same, unless someone overrides it for a
+    // call here, and thus obtaining the UI icu::Locale has to be done only
+    // once.
+    static thread_local LanguageTag aUITag( LANGUAGE_SYSTEM);
+    static thread_local icu::Locale aUILocale;
+
+    if (aUITag != rDisplayLanguage)
+    {
+        aUITag = rDisplayLanguage;
+        aUILocale = getIcuLocale( rDisplayLanguage);
+    }
+
+    icu::Locale aLocale( getIcuLocale( rLanguageTag));
+    icu::UnicodeString aResult;
+    aLocale.getDisplayName( aUILocale, aResult);
+    return OUString( reinterpret_cast<const sal_Unicode*>(aResult.getBuffer()), aResult.length());
+}
+
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