How to translate the "Search" word in the search box?

Hi, i'm using polylang for my multilanguage website (english/german) and i already tranlated my content with it and all other stuff with poedit ... but i really can't translate the word "Search" in the searchbox to "Suche". I tried to edit the searchform.php, but i doesn't work. A little help would be great. Thanks. Cheers Tom