When a new instance is created through linked_table the new instance uses the default locale. If the parent instance uses a non-default locale, the child instance should inherit the locale used in the parent form.

This could be implemented by passing _locale to the new instance (if one isn't provided in newInstanceKeyToValueMap) at the line linked below
https://github.com/odk-x/app-designer/blob/7abf14b16d940850cedfa66e2f9c2afd79553b3e/app/system/survey/js/prompts.js#L1035-L1038