Get error in comment and search box when activating this plugin

Your plugin works great in some ways but there is (called) defect that my customers can not fill in search boxes and comment boxes in Vietnamese words, which having tone marks. It only works well with word without tone marks, such as English.
And even keying English, the speed of keying is also lower than usual without activating your plugin. Generall, keying words works not smoothly as without activating!!

Pls test by fill in the search box at top-right of this site (having the alt text=’Tra cuu SP (go TV khong dau): https://trangthietbiytehcm.com/

btw, thanks for your promt reply when I first posted this issue on the review section!

The page I need help with: [log in to see the link]