Currently, the Wikidata Query Service has a suggestion for the following code snippet:

SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }

Once the mul language code is available on Wikidata, that should probably be changed to:

SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en,mul". }

as I assume the label service won’t take mul into account otherwise, but we want people to use queries that will see mul labels.

Other suggestions in the query service UI, and queries it makes internally, should also be updated in the same way.