Ok, eventually it seems to be all right, it's to easy to make mistakes.
Now, the only two things that you have to chek are:
/Sources/Subs.php
array(
'tag' => 'youtube',
'type' => 'unparsed_commas_content',
'test' => '\d+,\d+\]',
'content' => '<object type="application/x-shockwave-flash" width="$2" height="$3" data="http://www.youtube.com/v/$1"><param name="movie" value="http://www.youtube.com/v/$1"></param><param name="wmode" value="transparent"></param></object>',
'validate' => create_function('&$tag, &$data, $disabled', '
if (isset($disabled[\'url\']))
$tag[\'content\'] = \'$1\';'),
'disabled_content' => '<a href="$1" target="_blank">$1</a>',
),
array(
'tag' => 'hr',
'type' => 'closed',
'content' => '<hr />',
'block_level' => true,
),
And in Themes/default/languages/modifications.
Yourlanguage.php:
$txt['youtube'] = 'YouTube';
Don't understand where is the issue..there's no opportunity to make mistakes.