It seems to me that I’m translating you using complicated ways 
1. why do you need to upload a file? it is easier to immerse the full list of text in a hidden text box. another language in another hidden text box, etc. 2. you can ignore the json markup altogether. the sequence of lines separated by a sign (a group of characters or special characters) is easier to overtake into an array and work with it using the same algorithm.
Your method is 1. slow. 2. A lot of blocks 3. inconvenient when editing…
it’s easier this way:
textbox1 - full text in En
texbox2.- full text in Es
these are instead of files.
The method I proposed is more acceptable, working with files is more organized especially when the application is translated into many languages and translators know how to work with json files.
Another problem with your method is that you have to maintain the order of all the items in the list, if you no longer need a translation and you want to delete it, you will have to change all the indexes that come after it.
Also if I’m not mistaken, lists are kept in the RAM and the more languages the application is translated into, the more RAM your application will take up.