You can set a WPC MPU to display English in adjustments, but if you change batteries or ROMS, it reverts to whatever the board is jumpered for.

Early Sys11s had the language jumper (W7 IIRC), later ones needed a ROM change (U26 on some, U26 and U27 on others)

Regarding the quality of the repair, nowadays I either put in a zero ohm jumper to match, install DIP switches like the IJ and later games have, or just remove the other jumpers, since all out or all in = English

I do the same here - either a zero ohm link or dip switches. Just sounded like you weren't happy with the quality of your work...