let me apologize and correct my self, pinning is directly related to discussion board, board is directly related to language by design. So when you add a board to some language it will show that board only under the language that board was entered. I wan't able to reproduce the issue you have so please provide us with steps to reproduce the issue.
There was a bug related to board, topic and message pinning and it was resolved, so please specify the version you are using ? We can provide you with the latest version so you can upgrade if that is an option for you ?