I have been working with a Ukrainian student to help them practice English and have noticed in their writing they often end sentences with double parentheses. For example: "I went to the park yesterday))". Has anyone ever encountered this before or does anyone know where this came from? I'm unsure of how to correct it without embarrassing them, so any information I can get before I bring it up will be helpful.
Is this writing happening in some form of informal digital communication like texting? In some countries where Cyrillic is the alphabet of choice, emoticons (for example the :) smiley face) are written without the colon for the eyes to conserve SMS characters. It's very possible that your student is using these "eyeless emoticons" to express tone in the same way that a English speaker would end their texts with an emoji.
I struggle to find formal sources for this, but here is an article: https://www.rbth.com/lifestyle/326858-why-russians-use-parentheses
You could try gently asking them why they do it, and build on their explanation, which is unlikely to be convincing, because ending a sentence with double parentheses is always incorrect in English (or any other language that I have heard of). You end a sentence with one (only) of these: a period ('full stop'), question mark, or exclamation mark.
You have three options for punctuating the end of a sentence: a period, an exclamation mark, or a question mark