Since some time I am wondering what hybris thinks about adding out of the box languages to solr schema? I am sure for example spanish and also dutch are contained out of the box since at least two years and they are still not maintained in the solr schema.
Point is not that I dont know how to add them but I wonder how you sell this as a solution and do not care about such things (that can be easily fixed).
In case you dont want to preset those languages in solr I would propose that at least you would give a way of saying that you could configure for a language a kind of "solr schema language", so that way the indexed value for example would be in dutch but when creating the field name for solr we would use english so we would have applied the same index / search behaviour like for english - for sure thats not optimal but at least your index does not fail.
But honestly I would expect that you provide the correct solr schema for the OOTB languages you ship the platform.