To make sure that after editing previously created video module and adding new translations will not change currently used translation.
As you can see in this test, we have created video module with chinese translation and then edit this module by adding new translation.
[Logic is here](https://github.com/edx/edx-platform/blob/alex/multiple_transcripts_editor/common/lib/xmodule/xmodule/video_module/video_module.py#L118)