YouTube has millions of videos that their 1.3 billion viewers can't watch because the videos aren't in their language.
YouTube creates revenue for content creators/uploaders, leading to more content for its viewers, but it could also create translator accounts for people who could translate YouTube videos, and pay those people a percentage of the video's ad revenue when the viewer uses translations, based on the amount of translation they are responsible for.
Many videos are in languages (for example, Spanish) where there is usually a low payment need for labor, so working on translation might be appealing. Otherwise, people who work in or practice languages may provide translations more often because there is a possibility of revenue.
This would do two things for YouTube:
1) Quickly increase the amount of content their audience could chose from and watch, without increasing the burden of server costs.
2) Provide information to improve their automatic translation technology.
Both of these would increase revenue, of course.
If implemented, we might expect a quick rush to translate the most popular videos into other languages, because these would offer higher revenue to translator accounts.
Currently (if what I have read is current) YouTube does kind of the opposite. It offers creators the option to pay professional translation services to translate their content. (I'm not sure how much this service gets used.)