BCountry: add a GetPreferredLanguage method.

The APIs for this were introduced in ICU 63, so we'll need an update.
ICU 63 does not build with gcc2, so this method is disabled there.

Change-Id: Iabe49509ed6d4e578560d497d3ca336a97db4625
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1874
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: Jérôme Duval <[email protected]>

docs/user/locale/Country.dox

@@ -117,6 +117,19 @@
 */
 
 
+/*!
+	\fn status_t BCountry::GetPreferredLanguage(BLanguage& language) const
+	\brief Get the most likely language to use in that country.
+
+	\param language A reference to a BLanguage to set to the preferred language.
+
+	\returns A status code, B_OK if everything went fine, or an error code
+	         otherwise.
+
+	\since Haiku R1
+*/
+
+
 /*!
 	\fn const char* BCountry::Code() const
 	\brief Gets the ISO country code for the country.

headers/os/locale/Country.h

@@ -39,6 +39,7 @@ public:
 			status_t			GetName(BString& name,
 									const BLanguage* displayLanguage = NULL
 									) const;
+			status_t			GetPreferredLanguage(BLanguage&) const;
 
 			const char*			Code() const;
 									// ISO-3166

src/kits/locale/Country.cpp

@@ -139,6 +139,35 @@ BCountry::GetName(BString& name, const BLanguage* displayLanguage) const
 }
 
 
+status_t
+BCountry::GetPreferredLanguage(BLanguage& language) const
+{
+#if __GNUC__ == 2
+	return ENOSYS;
+#else
+	status_t status = InitCheck();
+	if (status != B_OK)
+		return status;
+
+	icu::Locale* languageLocale = fICULocale->clone();
+	if (languageLocale == NULL)
+		return B_NO_MEMORY;
+
+	UErrorCode icuError = U_ZERO_ERROR;
+	languageLocale->addLikelySubtags(icuError);
+
+	if (U_FAILURE(icuError))
+		return B_ERROR;
+
+	status = language.SetTo(languageLocale->getLanguage());
+
+	delete languageLocale;
+
+	return status;
+#endif
+}
+
+
 const char*
 BCountry::Code() const
 {