Separate tags with semicolon

The tag delimiter is made translatable:

$comma = _x( ',', 'tag delimiter' );

So this can be changed with a simple filter:

add_filter( 'gettext_with_context', 't5_semicolon_tag_delimiter', 10, 4 );

function t5_semicolon_tag_delimiter( $translated, $text, $context, $domain )
{
    if ( 'default' !== $domain or 'tag delimiter' !== $context or ',' !== $text )
        return $translated;

    return ';';
}

Install as plugin; works without any side effects.

What is tricky: changing the string Separate tags with commas to say semicolon. You cannot use the same solution, because you don’t know the language of your users. Not sure how to handle that.