PHP: How do I detect if an input string is Arabic

Use regular expression for shorter and easy answer

 $is_arabic = preg_match('/\p{Arabic}/u', $text);

This will return true (1) for arabic string and 0 for non arabic string

this will check if the string is Arabic Or has Arabic text

text must be UNICODE e.g UTF-8

$str = "بسم الله";
if (preg_match('/[اأإء-ي]/ui', $str)) {
    echo "A match was found.";
} else {
    echo "A match was not found.";
}

I assume that in 99% of cases, it is enough to check that string contains Arabic letters and does not consist of all of them.

My core assumption is that if it contains at least two or three Arabic letters, the reader should know how to read it.

You can use a simple function:

<?php
/**
 * Return`s true if string contains only arabic letters.
 *
 * @param string $string
 * @return bool
 */
function contains_arabic($string)
{
    return (preg_match("/^\p{Arabic}/i", $string) > 0);
}

Or if the regex classes do not work:

function contains_arabic($subject)
{
    return (preg_match("/^[\x0600-\x06FF]/i", $subject) > 0);
}

I would use regular expressions to get the number of Arabic characters and compare it to the total length of the string. If the text is for instance at least 60% Arabic charactes, I would consider it as mainly Arabic and apply RTL formatting.

/**
 * Is the given text mainly Arabic language? 
 *
 * @param string $text string to be tested if it is arabic. :-)
 * @return bool 
 */
function ct_is_arabic_text($text) {
    $text = preg_replace('/[ 0-9\(\)\.\,\-\:\n\r_]/', '', $text); // Remove spaces, numbers, punctuation.
    $total_count = mb_strlen($text); // Length of text
    if ($total_count==0)
        return false;
    $arabic_count = preg_match_all("/[اأإء-ي]/ui", $text, $matches); // Number of Arabic characters
    if(($arabic_count/$total_count) > 0.6) { // >60% Arabic chars, its probably Arabic languages
        return true;
    }
    return false;
}

For inline RTL formatting, use CSS. Example class:

.embed-rtl {
 direction: rtl;
 unicode-bidi: normal;
 text-align: right;
}

I'm not aware of a PHP solution for this, no.

The Google Translate Ajax APIs may be for you, though.

Check out this Javascript snippet from the API docs: Example: Language Detection

I assume you're referring to a Unicode string... in which case, just look for the presence of any character with a code between U+0600–U+06FF (1536–1791) in the string.

public static function isArabic($string){
    if(preg_match('/\p{Arabic}/u', $string))
        return true;
    return false;
}

The PHP Text_LanguageDetect library is able to detect 52 languages. It's unit-tested and installable via composer and PEAR.

This function checks whether the entered line/sentence is arabic or not. I trimmed it first then check word by word calculating the total count for both.

function isArabic($string){
        // Initializing count variables with zero
        $arabicCount = 0;
        $englishCount = 0;
        // Getting the cleanest String without any number or Brackets or Hyphen
        $noNumbers = preg_replace('/[0-9]+/', '', $string);
        $noBracketsHyphen = array('(', ')', '-');
        $clean = trim(str_replace($noBracketsHyphen , '', $noNumbers));
        // After Getting the clean string, splitting it by space to get the total entered words 
        $array = explode(" ", $clean); // $array contain the words that was entered by the user
        for ($i=0; $i <= count($array) ; $i++) {
            // Checking either word is Arabic or not
            $checkLang = preg_match('/\p{Arabic}/u', $array[$i]);
            if($checkLang == 1){
                ++$arabicCount;
            } else{
                ++$englishCount;
            }
        }
        if($arabicCount >= $englishCount){
            // Return 1 means TRUE i-e Arabic
            return 1;
        } else{
            // Return 0 means FALSE i-e English
            return 0;
        }
    }