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JavaScript

function isPalindrome(str) {
  var splitted = [...str.toLowerCase().replace(/\s/g,'')];
  return splitted.join`` === splitted.reverse().join``;
}

console.log(true === isPalindrome('Аргентина манит негра'));
console.log(true === isPalindrome('Аргентинаманитнегра'));
console.log(false === isPalindrome('Агрентинаманитнегра'));
console.log(false === isPalindrome('Аргентинаi манит негра'));