CX2 has significant architecture changes with respect to CX1, making the translations they produce non compatible. That is, editing with CX2 a translation started with CX1 (or the other way around) is expected to be problematic.
In order to allow both CX1 and CX2 to coexist, we can keep their content separate. That is, translations started with CX1 will be always edited with CX1 editor, and those started with CX2 will always be edited with CX2. Regardless of which is the default translation editor at the time.
As a prerequisite to support this ticket, we need to complete first T187986: CX2: Register the version used to start a translation