Hi, this is the function I use to convert string to "search engine friendly URLs":

setlocale( LC_CTYPE, 'en_GB.utf8' );
header( 'Content-Type: text/html; charset=utf-8' );

function translit( $str )
{
	$str_trans = iconv( 'UTF-8', 'ASCII//TRANSLIT', $str );
	for ( $i = 0; $i < strlen( $str_trans ); $i++ )
	{
		$chr1 = $str_trans[$i];
		$chr2 = mb_substr( $str, $i, 1 );
		$str_res .= ( $chr1 == '?' ) ? $chr2 : $chr1;
	}
	return $str_res;
}

function strtourl( $str, $seperator = '-', $case = MB_CASE_LOWER, $translit = true ) {
	
	# Validate and sanitise input
	if( strlen ( $str ) < 1 )
		trigger_error( 'First argument must be one or more characters', E_USER_ERROR );
	if( !in_array( $seperator, array( "-", "_", "+" ) ) )
		trigger_error( 'Second argument must by a hyphen, underscore or plus sign', E_USER_ERROR );
	$str = trim( $str );
	$str = strip_tags( $str );
	$flags = ( int ) $case;
	
	# Transliterate
	if( $translit == true )
	{
		if( function_exists( 'transliterate' ) )
			$str = transliterate( $str, array( 'han_transliterate', 'jamo_transliterate', 'greek_transliterate', 'hebrew_transliterate', 'cyrillic_transliterate' ), 'UTF-8', 'UTF-8' );
		if( function_exists( 'iconv' ) )
			$str = translit( $str );
	}
	
	var_dump( $str );
	
	# Clean ampersands, whitespace and punctuation
	$patterns = array( "/[&|&#][a-zA-Z0-9]{2,7}[;]/", "/\s{2,}/", "/[\t\r\n\v\f]+/", "/[\"`¬!£$%^%&*()={}\[\]#~'@;:.>,<|\/?\\\]+/" );
	$replacements = array( "", " ", " ", "" );
	$str = preg_replace( $patterns, $replacements, $str );
	
	# Replace and spaces with seperators
	$str = str_replace( ' ', $seperator, $str );
	$str = preg_replace( "/$seperator{2,}/", $seperator, $str );
	
	# Convert case
	$str = mb_convert_case( $str, $case, 'UTF-8' );
	
	return $str;
		
}

echo strtourl( 'slug semlabs.co.uk Some text & and AmPersand', '-', MB_CASE_LOWER, true );
echo strtourl( 'slug semlabs.co.uk Some text & and AmPersand', '-', MB_CASE_TITLE, false );

It has a couple of extra features, namely it uses multi-byte case convert, which changes the case of characters with accents and you can also use transliteration for removing any accents if you just want ASCII URL slugs.

I think the reason the above mod_rewrite rules don't work is because they are for WordPress. Try one of these instead:

RewriteRule ^(.+)$ $1.html [QSA]

RewriteRule ^([a-zA-Z0-9_-\x7f-\xff]+)$ $1.html [QSA]

If you use that transliteration, ensure you have a locale defined. Othewise some characters won't come out properly.

Could you provide more specific details as to what you are having trouble with. Try searching the files using a find facility in a text editor to search for the relevant parts.