You can use the Encode module to convert chars between charsets. It is also possible to replace chars, that are represented in one charset, but not in another. With Encode::encode or Encode::from_to. Another idea is to remove unknown chars with

s/[\x80-\xff]//g;

# or
y/\x80-\xff//d;

# or
Encode::from_to($string, 'utf-8', 'us-ascii', 0 );
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or you may translate the chars by yourself ie:

s/ö/oe/g;
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