如何使用str_replace与数组或缩短正则表达式和PHP而不是重复三次？

I have the following which replace all of å, ø, æ .... etc to just _.

$string = strtolower($string);
$regexp = '/( |å|ø|æ|Å|Ø|Æ|Ã¥|ø|æ|Ã…|Ø|Æ)/iU';
$replace_char = '_';
$data = preg_replace($regexp, $replace_char, $string);

Now I want to change them to according to the followings.

Replace,

space to _

å, Å, Ã¥ and Ã… to a,

ø, Ø, à and ظ to o,

æ, Æ, æ and Æ to e.

Can I use str_replace with array to do it? If yes, how to?

Or do I have to repeat the same regex three times?

Could anyone tell me better way to write the code?

--EDIT--

Pleas ignore the encoding at the moment. I am NOT asking advices about encoding now.

I asked the encoding problem here. Norwegian characters problem

I would use strtr that you can pass a mapping:

$mapping = array(
    'å' => 'a', 'Å' => 'a', 'Ã¥' => 'a', 'Ã…' => 'a',
    'ø' => 'o', 'Ø' => 'o', 'Ã' => 'o', 'Ø' => 'o',
    'æ' => 'e', 'Æ' => 'e', 'æ' => 'e', 'Æ' => 'e'
);
$str = strtr($str, $mapping);

But you should rather fix your encoding issue before. Because then you could use transliteration with iconv:

$str = iconv("UTF-8", "ISO-8859-1//TRANSLIT", $str);

Like Gumbo said, you have some troubles with encoding, but leaving this fix to you the general idea would be

$data=preg_replace('/[ åøæÅØÆ]/iu','_',mb_strtolower($string,'utf-8'));

Note the mb_ variant of strtolower, in case you want to work with unicode.

Edit: And stakx's suggestion also makes sense, but it changes the logic.

An alternative solution utilizing mappings is to use str_replace. I used a minimal set of your mappings for an example. Each value of $search maps to the corresponding index in $replace.

$search = array(' ', 'å', 'ø', 'æ', 'Å', 'Ø','Æ','Ã¥');
$replace = array('_', 'a', 'o', 'e', 'a', 'o', 'e', 'a');
$string = str_replace($search, $replace, mb_strtolower($string, 'utf-8');