I see, I guess they have some sort of a list to which field goes to which label.
Searching these shouldn’t be an issue. However I don’t know if this type of structure is usable for meta-type filtering, as each value is also associated to a separate field (as far as I can tell), and that’s something I have not seen before in the past 15 years. So for example instead of having a single “languages” field to store the languages for each post, there is multiple completely separate fields scattered like “_checkbox-1”, “_checkbox-2” which signify which languages the given post is associated to. So if you were to make a checkbox filter for that, it’s very problematic, as each checkbox should also be attached to a different meta key, which is not how meta filters work.
Normally you make a filter for the “languages” field and filter plugins will fetch the values for that field across the database and generate a checkbox filter for it. But here every checkbox is tied to a different field and a different value, which is something no plugin search/filter can deal with.
Their out of the box solution is likely coded to this exact structure.