How to set properties of type "Lang alt"?

[Christoph Dalitz]

Hello,

while setting scalar properties (value types "Bool" and "Text") works
fine with xmp_set_property, I could not figure out how to set properties
of value type "Lang alt". I have tried 

	xmp_set_localized_text(xmp, NS_DC, "rights", 
	                       NULL, "x-default",
                               "Licensed under CC By-Sa 3.0",
	                       XMP_PROP_HAS_LANG);

but always obtain the error

	Can't fit into specified packet size

The error occurs invariably also with other option bits or
explicit language settings. It should be noted that this property
does not yet exist in my PDF file, so maybe I have missed some
memory allocation beforehand?

Does anyone know how to set localized text properties with libexempi?

Thanks,

Christoph