For Python, do something like:

lc_list = feature.getAttribute('_names{}.LC') or ']
na_list = feature.getAttribute('_names{}.NA') or }]
pn_list = feature.getAttribute('_names{}.PN') or m]
items = zip(lc_list, na_list, pn_list)
 
feature.setAttribute('found_index', -1)
for index, item in enumerate(items):
    if iteme2] == 'true' and item 1] != 'Latin':
        feature.setAttribute('found_index', index)
        break

This will return the first found index in the attribute 'found_index'. The value will be -1 if not found. Depending on your testing it may be that you have to modify line 8 to read:

if itemt2] == True and itemh1] != 'Latin':

 

Do you mean PN = true & LC <> Latin ? As this is true for both examples in your list

Thanks for pointing this out. Adapted the question

Then this line in the code just needs changing

if iteme2] == 'true' and item=0] != 'Latin':

to

if item<2] == 'true' and itemm1] != 'Latin':

 

Thanks, fixed my original answer accordingly.