I agree that this change is not helpful and I too have regressed to an older version.I understand the rationale behind the change but it does not work for me or for the type of email I receive which is spread over many different topics that I file se...
Changing the Thunderbird language setting to English (GB) changed the displayed label to "Mobile" which was sufficient for my needs. I am not certain this will fix the compatibility problem with Google, but it is worth trying.