i want to replace English number with Devanagari number and add some code in function.php of theme and it works on theme but doesn't work on plugin can you please guide me how can i replace English number . 

the code i have use

function make_nep_number( $str ) {
$engNumber = array(1,2,3,4,5,6,7,8,9,0);
$nepNumber = array("१","२","३","४","५","६","७","८","९","०");
$converted = str_replace($engNumber, $nepNumber, $str);

return $converted;
}

add_filter( 'comments_number', 'make_nep_number' );