I am not sure how LO draws upon locale settings for displaying this type of information.
You can customise the dialog used via Tools > Options… > LibreOffice > General > Open/Save dialogs section > uncheck “Use LibreOffice dialogs”. Now LO will use the system dialog. You have indicated though that you require the LibreOffice version of this dialog in order to use the CMIS function.
I cannot find any bug or enhancement request relating to this particular aspect of LO. Please file an enhancement bug and provide as much information as possible. Don’t forget to mark your bug as an ‘enhancement’. The QA team will be happy to help you triage your feature request in the bugtracker.
Please post a link to any bugs you file in a comment below using the format “fdo#123456”.