Update to 4.50.4 - resource string not found - Language ID = 3

After an update from 4.3 to 4.50.4
I get a log full of "resource string not found" (...) finished with "Language ID = 3"

How could I solve this ?

Thank you for your kind assistance !

Did you also "update" the database?
How many Languages do you have? What are there Ids?