Unique ID Widget: Why does the widget submits the same value on some submissions?

The unique ID's work properly when the respondent completes the form in the
"original" language (English). If someone with the same email completes the
form twice, it still gives them the same unique ID. However, if someone
completes it in Spanish multiple times, it gives them a different Unique ID
every time.

Apologies for the inconveniences this may have caused to you. 

I have been testing a cloned form of yours and I can see the displayed ID is different no matter the language selected, I have tested using always the same information, here is a screenshot of what I can see on my end: 

I noticed the correct ID displays on the submissions page as well. Please note that the unique ID widget will always generate a different value no matter the selected language. 

May you please test on your form again and check if the generated IDs are indeed different or it they are the same? 

So far, your submissions show different IDs. 

Please let us know if the issue persists. 

It was definitely assigning the same unique ID's before, but now it's not.
It may have been before I changed the text into Spanish as well.

...

Your form has only four submissions and each submission has a different ID. I also saw that you deleted your other submissions, so we are unable to check them. 

If the same issue happens again, let us know, but do not delete the submissions with the same Unique ID. 

I case that your form is embedded and the same Unique ID is generated when the embedded form is submitted, provide us the webpage URL, so that we can test the embedded form.