AppleScript tell application "Finder" can't use special characters
I fixed it by decoding the umlauts like this:
considering case
    set mylocation to searchReplace(mylocation, &quot;Ä&quot;, &quot;%C3%84&quot;)
    set mylocation to searchReplace(mylocation, &quot;ä&quot;, &quot;%C3%A4&quot;)
    set mylocation to searchReplace(mylocation, &quot;Ö&quot;, &quot;%C3%96&quot;)
    set mylocation to searchReplace(mylocation, &quot;ö&quot;, &quot;%C3%B6&quot;)
    set mylocation to searchReplace(mylocation, &quot;Ü&quot;, &quot;%C3%9C&quot;)
    set mylocation to searchReplace(mylocation, &quot;ü&quot;, &quot;%C3%BC&quot;)
    set mylocation to searchReplace(mylocation, &quot;ß&quot;, &quot;%C3%9F&quot;)
    set mylocation to searchReplace(mylocation, &quot;ẞ&quot;, &quot;%E1%BA%9E&quot;)
end considering