Hi Skerdi,
I have managed to test and reproduce this issue. I consider it a bug, since an identifier is not a translatable element, and users should be able to generate unique identifiers in a multilingual site. Consequently, I have filed a bug ticket here:
I have added it to our internal list of bugs for review before the next release. However, at this time we're working on wrapping up the 2.4.1 release, so it's possible it won't be addressed then. For bug fixes, we try to fix as many as we can before each public release, but it depends on time available and the complexity of the bug. You can read more about how we manage the AtoM project here:
If this is a critical issue for your institution and you would like to guarantee its inclusion in the next public release, then your institution might consider sponsoring a fix for the issue. If this is of interest, please feel free to contact me off-list, and we can prepare a development estimate for you.
In the meantime, I'm not sure what to recommend as a workaround. You can check the counter position in the primary language prior to flipping the interface to Greek and generating a new identifier, and then manually edit the identifier, and manually edit the counter value in Settings. Obviously this is not ideal, however. I guess you could also use a shared spreadsheet or something external to AtoM to keep track of your new identifiers.
Hopefully we'll be able to address this issue soon.
Regards,