It would be really neat to be able to sort collections on the language variations as well.
If we take our Product collection as an example. We have products that have languages (which corresponds to our markets), and for each language, a product can be set to enabled or disabled with a boolean. In this case, it would be nice to be able to sort the list on products that are enabled for a certain locale or language, eg. Products enabled for our Swedish locale. See image. Without the locale filter, I would get the enabled products for the default locale I presume.
Example of how it could look: