Should mentioning the Operating System in titles be removed?
We have tags to indicate those information. And on Stack Overflow it is recommended to remove the language tag from the title.
The operating system should be included in the title if it's an important requirement. It often is.
It is not recommended to remove the name of the language on Stack Overflow! I think you're confusing this with the recommendation not to include language names as “tags” in titles. That is:
A title of the form “Application type with key characteristic on platform” is perfectly reasonable for SR.SE.
Here's the easy rule:
Cover the tags, and ask yourself if the title conveys enough information. It needs to.
That means two things:
Tags are for filtering, not for completing otherwise incomplete titles.
The answer from Gilles in Why do people insist titles actually be a question (I seem to be unable to find a “share” link on the specific answer…) refers to a meta.SO FAQ with a scientifically-based highest-scored answer on titles.
The part interesting here is: Do not copy parts of the question in the title.