Hi Martin,
You should be able to extend the 'Where condition' in the UniSelector component (in Page Type -> Fields) with the the culture of the currently created document. Something like this should do the job:
ClassName = 'custom.Location' and DocumentCulture = '{% EditedObject.DocumentCulture #%}'
It's important to add this as macro and not as simple text in where condition because in that case culture of current document won't be resolved. To achieve that, simply click on the blue arrow on the left side near 'Where condition' label and place the condition inside the popup window.
Best regards,
Dragoljub