The 008 is the field we would prefer to use for the language facet and no other field. The 008 only field is consistently used in all our records. We stopped using the 240 fields in bib records, because that caused problems in Vega. The only time we use the 041 is when a title is bilingual. It would be a huge amount of work to update all our bib records. It is complicated how it currently works, and search results are confusing.