Sometime json_encode not working in uft8 content so this is very common problem , In this article it will solve this problem. This is simple code which help you.

<?php
$data = [
    'গুগলের ‘স্টাইল আইডিয়াস’',
    'ফেসবুকের নয়া উদ্যোগে'
];
echo "<pre>";
print_r($data);
echo "<br>";
echo json_encode($data); // normal json_encode
echo "<br>";
echo json_encode($data, JSON_UNESCAPED_UNICODE); // json_encode with extra parameter which Encode multibyte Unicode characters literally

Then output is :

This is array data:

print_r($data);
Array
(
    [0] => গুগলের ‘স্টাইল আইডিয়াস’
    [1] => ফেসবুকের নয়া উদ্যোগে
)

This is normal json_encode

echo json_encode($data);
output will be is:

["\u0997\u09c1\u0997\u09b2\u09c7\u09b0 \u2018\u09b8\u09cd\u099f\u09be\u0987\u09b2 \u0986\u0987\u09a1\u09bf\u09df\u09be\u09b8\u2019","\u09ab\u09c7\u09b8\u09ac\u09c1\u0995\u09c7\u09b0 \u09a8\u09df\u09be \u0989\u09a6\u09cd\u09af\u09cb\u0997\u09c7"]

json_encode with JSON_UNESCAPED_UNICODE

echo json_encode($data, JSON_UNESCAPED_UNICODE);
output will be: 

["গুগলের ‘স্টাইল আইডিয়াস’","ফেসবুকের নয়া উদ্যোগে"]

If you face this problem then use this code which help you, if you face any problem then please inform me. I will try to help you.