Trustfully write anything in your language. Stop worrying about truncated content.
Full UTF-8 adds complete support for any UTF-8 character. Without this plugin, WordPress truncates anything after the first 4-bytes-long UTF-8 character.
Suppose you copy some text from a web page and paste it into the editor. You see everything is fine, so you hit save. As soon as the page is reloaded, you find out that your post has been truncated at a point that seems to be quite random. Well, that's not random. The breaking point is the position of the first 4-bytes-long UTF-8 character. Anything from that one up to the end of the post is irremediably lost forever.
You definitely need to install this plugin if you write 4-bytes-long UTF-8 characters. How do you know that? Many Chinese characters, musical and mathematical symbols and Emoji icons are 4-bytes-long. But you can always try to draw something and check for yourself. If you get a Unicode hexadecimal value with more than four digits after 0x then it is a 4-bytes-long UTF-8 character. For example, a G-clef is one because 0x1D11E has 5 digits after 0x.