http://play.golang.org/p/ls96RxJxpz

    "੧".match(/\d/); //null

Doesn't in Ruby:

/\d/.match "੧" #=> nil

  \d         A digit: [0-9]
  \p{Digit}  A decimal digit: [0-9]

  ab1234567890cd matched 1234567890
  ab𝟣𝟤𝟥𝟦𝟧𝟨𝟩𝟪𝟫𝟢cd no match

EDIT: and perhaps more surprising to see in the logs:

  Exception in thread "main" java.lang.NumberFormatException: For input string: "𝟤𝟥𝟦𝟧"
  	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
  	at java.lang.Integer.parseInt(Integer.java:449)

    NSString *pattern = @"\\d", *string = @"੧";
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern
                                                                           options:NSRegularExpressionCaseInsensitive
                                                                             error:nil];

    NSUInteger numMatches = [regex numberOfMatchesInString:string
                                                   options:0
                                                     range:NSMakeRange(0, [string length])];

    numMatches ? NSLog(@"%@ found by %@", string, pattern) : NSLog(@"%@ not found", string);

    // 2013-05-20 09:38:42.650 Regexperiment[17848:c07] ੧ found by \d