s( ("[^"]*")     # a quoted field, or standalone part of a field
      | (?<![^;])    # start of line or preceded by semicolon = start of field
        ( [\-\d,]+   # characters most likely forming a number
          | ([?]) )  # or a "?" 
        (?![^;])     # end of line or followed by semicolon  = end of field
    )                # end of regex, start of substitution
    {
        $1 or        # replace quoted string by itself = skip
        $3 ? ''      # a bare unquoted '?', delete
        : do { (my $number = $2)   # must be a number
              =~ tr/,/./;       # replace ',' with '.'
            $number }           # return value
    }xge;