One goal of the new Content Translation data collection (T231316) is to help differentiate the impact of the system's different entry points. As a result, the content_translation_event schema has a different event_source value for each entry point, for use with dashboard_open and dashboard_translation_start events.
As part of T286641, several new entry points to Content Translation will be added. Each of these entry points will likely require a new event_source value, which will have to added to the schema and to the schema readme.