if you only need it in product page, so you can try adding this code to the bottom of "themes/niara/js/product.js"
window.addEventListener('DOMContentLoaded', (event) => {
const lang = document.documentElement.getAttribute('lang');
if (lang === 'en-us') {
document.querySelector('.unit-price').innerHTML = document.querySelector('.unit-price').innerHTML.replace('per meeter', 'for meter');
} else if (lang === 'tk') {
document.querySelector('.unit-price').innerHTML = document.querySelector('.unit-price').innerHTML.replace('per meeter', 'for meter in tk');
}
});