No column header derives from the field name.
The only defined starting point is a fresh installation where the definitions from the installation are transferred to a file called columns.ini which is a local, user-defined file for the column definitions.
This file only gets created during a(nother) fresh installation and is kept when doing an update installation or changing the GUI language at runtime.
I would like to draw your attention to the flexible features of MP3tag.
While the default installation really only features columns for standard fields and file properties it is possible for the user to define his own columns like e.g. one for the playlist name in which he has used the file, an indicator that a file should be deleted, a user-defined field to store the order number of a Bach cantata and so on.
There will never be a decent translation for these user-defined columns.
Or a user modifies value, field and sort-by option of a column definition but keeps the header - is this a user-defined column or the original that should be translated?
We can cut this short: you are free to keep your opinion that this is a bug.
It has been rated as no bug until now, the technicalities have been laid open.