@tolo1978, the same problem is explained here Doesn't save changes articles - #2 by dmasta with a workaround. The problem seems to be related with the imporexport tool because the locale field is recorded with NULL.
I have opened this issue importexport fails filling the locale column in submissions table. Users can't edit metadata in submissions. · Issue #7636 · pkp/pkp-lib · GitHub but I’m not php expert so it is hard for me to solve it.