Using setlocale() doesn't affect PHPs number conversions

I have the following script:

<?php
 $test = "2.5";
 echo (float)$test;
 echo "\n";

 $r = setlocale(LC_ALL, "da_DK.UTF8");
 setlocale(LC_ALL, NULL);
 print_r(localeconv());
 echo "\n";
 echo (float)$test;
 echo "\n";
 echo (float)"2,5";
 echo "\n";
?>

Which generates the following output:

2.5
Array
(
    [decimal_point] => ,
    [thousands_sep] => .
    [int_curr_symbol] => DKK 
    [currency_symbol] => kr
    [mon_decimal_point] => ,
    [mon_thousands_sep] => .
    [positive_sign] => 
    [negative_sign] => -
    [int_frac_digits] => 2
    [frac_digits] => 2
    [p_cs_precedes] => 1
    [p_sep_by_s开发者_Go百科pace] => 2
    [n_cs_precedes] => 1
    [n_sep_by_space] => 2
    [p_sign_posn] => 4
    [n_sign_posn] => 4
    [grouping] => Array
        (
            [0] => 3
            [1] => 3
        )

    [mon_grouping] => Array
        (
            [0] => 3
            [1] => 3
        )

)

2,5
2

The very last line which reads 2 - I would have expected that to read 2,5 - and as far as I can see on the PHP documentation, it should.

If the second call to setlocale is omitted then the output of localeconv() is inconsistent with the danish locale - for reasons that are unclear to me.

(float)"2,5" equals 2 (note the comma) whereas (float)"2.5" equals 2.5. The reason can be read in the manual:

If the string does not contain any of the characters '.', 'e', or 'E' and the numeric value fits into integer type limits (as defined by PHP_INT_MAX), the string will be evaluated as an integer. In all other cases it will be evaluated as a float.

Type casting is not affected by setlocale().