In the taxonomy of species, there are several components required to make a “valid” description for a taxon. They are the “taxon name”, the author, and the publication. The publication itself has its own components, among them is the name of the publication and the date of publication. They map neatly to what Wikidata uses for sources. It is however not a source and it should not be treated as a source.
A source asserts that something is true. There can be many sources that make such assertions. What they all do in taxonomy is refer to the original publication. A publication includes the formal description of a taxon. There are only two languages allowed for a formal description; they are Latin and English.
When publications are treated as sources, it is hard / not possible to distinguish them from other sources. Consequently the data loses its relevance as the information that makes up a valid description becomes incomplete.