Translit file names to simple chars, this prevent WordPress to allow accents and special chars at file names that breaks in some server's configuration.

wp_sanitize_file_name.php

/*
* Translit file names to simple chars,
* this prevent accents and special chars at file names.
***********************************************************************/
function my_sanitize_file_name($filename) {
	return remove_accents($filename);
}
add_filter('sanitize_file_name', 'my_sanitize_file_name');

/*
* Translit file names to simple chars,
* this prevent accents and special chars at file names.
***********************************************************************/
function my_sanitize_file_name($filename) {
	$rules = array(
		// Numeric characters
		'¹' => 1,
		'²' => 2,
		'³' => 3,

		// Latin
		'º' => 0,
		'°' => 0,
		'æ' => 'ae',
		'ǽ' => 'ae',
		'À' => 'A',
		'Á' => 'A',
		'Â' => 'A',
		'Ã' => 'A',
		'Å' => 'A',
		'Ǻ' => 'A',
		'Ă' => 'A',
		'Ǎ' => 'A',
		'Æ' => 'AE',
		'Ǽ' => 'AE',
		'à' => 'a',
		'á' => 'a',
		'â' => 'a',
		'ã' => 'a',
		'å' => 'a',
		'ǻ' => 'a',
		'ă' => 'a',
		'ǎ' => 'a',
		'ª' => 'a',
		'@' => 'at',
		'Ĉ' => 'C',
		'Ċ' => 'C',
		'ĉ' => 'c',
		'ċ' => 'c',
		'©' => 'c',
		'Ð' => 'Dj',
		'Đ' => 'Dj',
		'ð' => 'dj',
		'đ' => 'dj',
		'È' => 'E',
		'É' => 'E',
		'Ê' => 'E',
		'Ë' => 'E',
		'Ĕ' => 'E',
		'Ė' => 'E',
		'è' => 'e',
		'é' => 'e',
		'ê' => 'e',
		'ë' => 'e',
		'ĕ' => 'e',
		'ė' => 'e',
		'ƒ' => 'f',
		'Ĝ' => 'G',
		'Ġ' => 'G',
		'ĝ' => 'g',
		'ġ' => 'g',
		'Ĥ' => 'H',
		'Ħ' => 'H',
		'ĥ' => 'h',
		'ħ' => 'h',
		'Ì' => 'I',
		'Í' => 'I',
		'Î' => 'I',
		'Ï' => 'I',
		'Ĩ' => 'I',
		'Ĭ' => 'I',
		'Ǐ' => 'I',
		'Į' => 'I',
		'IJ' => 'IJ',
		'ì' => 'i',
		'í' => 'i',
		'î' => 'i',
		'ï' => 'i',
		'ĩ' => 'i',
		'ĭ' => 'i',
		'ǐ' => 'i',
		'į' => 'i',
		'ij' => 'ij',
		'Ĵ' => 'J',
		'ĵ' => 'j',
		'Ĺ' => 'L',
		'Ľ' => 'L',
		'Ŀ' => 'L',
		'ĺ' => 'l',
		'ľ' => 'l',
		'ŀ' => 'l',
		'Ñ' => 'N',
		'ñ' => 'n',
		'ʼn' => 'n',
		'Ò' => 'O',
		'Ô' => 'O',
		'Õ' => 'O',
		'Ō' => 'O',
		'Ŏ' => 'O',
		'Ǒ' => 'O',
		'Ő' => 'O',
		'Ơ' => 'O',
		'Ø' => 'O',
		'Ǿ' => 'O',
		'Œ' => 'OE',
		'ò' => 'o',
		'ô' => 'o',
		'õ' => 'o',
		'ō' => 'o',
		'ŏ' => 'o',
		'ǒ' => 'o',
		'ő' => 'o',
		'ơ' => 'o',
		'ø' => 'o',
		'ǿ' => 'o',
		'º' => 'o',
		'œ' => 'oe',
		'Ŕ' => 'R',
		'Ŗ' => 'R',
		'ŕ' => 'r',
		'ŗ' => 'r',
		'Ŝ' => 'S',
		'Ș' => 'S',
		'ŝ' => 's',
		'ș' => 's',
		'ſ' => 's',
		'Ţ' => 'T',
		'Ț' => 'T',
		'Ŧ' => 'T',
		'Þ' => 'TH',
		'ţ' => 't',
		'ț' => 't',
		'ŧ' => 't',
		'þ' => 'th',
		'Ù' => 'U',
		'Ú' => 'U',
		'Û' => 'U',
		'Ũ' => 'U',
		'Ŭ' => 'U',
		'Ű' => 'U',
		'Ų' => 'U',
		'Ư' => 'U',
		'Ǔ' => 'U',
		'Ǖ' => 'U',
		'Ǘ' => 'U',
		'Ǚ' => 'U',
		'Ǜ' => 'U',
		'ù' => 'u',
		'ú' => 'u',
		'û' => 'u',
		'ũ' => 'u',
		'ŭ' => 'u',
		'ű' => 'u',
		'ų' => 'u',
		'ư' => 'u',
		'ǔ' => 'u',
		'ǖ' => 'u',
		'ǘ' => 'u',
		'ǚ' => 'u',
		'ǜ' => 'u',
		'Ŵ' => 'W',
		'ŵ' => 'w',
		'Ý' => 'Y',
		'Ÿ' => 'Y',
		'Ŷ' => 'Y',
		'ý' => 'y',
		'ÿ' => 'y',
		'ŷ' => 'y',

		// Russian
		'Ъ' => '',
		'Ь' => '',
		'А' => 'A',
		'Б' => 'B',
		'Ц' => 'C',
		'Ч' => 'Ch',
		'Д' => 'D',
		'Е' => 'E',
		'Ё' => 'E',
		'Э' => 'E',
		'Ф' => 'F',
		'Г' => 'G',
		'Х' => 'H',
		'И' => 'I',
		'Й' => 'J',
		'Я' => 'Ja',
		'Ю' => 'Ju',
		'К' => 'K',
		'Л' => 'L',
		'М' => 'M',
		'Н' => 'N',
		'О' => 'O',
		'П' => 'P',
		'Р' => 'R',
		'С' => 'S',
		'Ш' => 'Sh',
		'Щ' => 'Shch',
		'Т' => 'T',
		'У' => 'U',
		'В' => 'V',
		'Ы' => 'Y',
		'З' => 'Z',
		'Ж' => 'Zh',
		'ъ' => '',
		'ь' => '',
		'а' => 'a',
		'б' => 'b',
		'ц' => 'c',
		'ч' => 'ch',
		'д' => 'd',
		'е' => 'e',
		'ё' => 'e',
		'э' => 'e',
		'ф' => 'f',
		'г' => 'g',
		'х' => 'h',
		'и' => 'i',
		'й' => 'j',
		'я' => 'ja',
		'ю' => 'ju',
		'к' => 'k',
		'л' => 'l',
		'м' => 'm',
		'н' => 'n',
		'о' => 'o',
		'п' => 'p',
		'р' => 'r',
		'с' => 's',
		'ш' => 'sh',
		'щ' => 'shch',
		'т' => 't',
		'у' => 'u',
		'в' => 'v',
		'ы' => 'y',
		'з' => 'z',
		'ж' => 'zh',

		// German characters
		'Ä' => 'AE',
		'Ö' => 'OE',
		'Ü' => 'UE',
		'ß' => 'ss',
		'ä' => 'ae',
		'ö' => 'oe',
		'ü' => 'ue',

		// Turkish characters
		'Ç' => 'C',
		'Ğ' => 'G',
		'İ' => 'I',
		'Ş' => 'S',
		'ç' => 'c',
		'ğ' => 'g',
		'ı' => 'i',
		'ş' => 's',

		// Latvian
		'Ā' => 'A',
		'Ē' => 'E',
		'Ģ' => 'G',
		'Ī' => 'I',
		'Ķ' => 'K',
		'Ļ' => 'L',
		'Ņ' => 'N',
		'Ū' => 'U',
		'ā' => 'a',
		'ē' => 'e',
		'ģ' => 'g',
		'ī' => 'i',
		'ķ' => 'k',
		'ļ' => 'l',
		'ņ' => 'n',
		'ū' => 'u',

		// Ukrainian
		'Ґ' => 'G',
		'І' => 'I',
		'Ї' => 'Ji',
		'Є' => 'Ye',
		'ґ' => 'g',
		'і' => 'i',
		'ї' => 'ji',
		'є' => 'ye',

		// Czech
		'Č' => 'C',
		'Ď' => 'D',
		'Ě' => 'E',
		'Ň' => 'N',
		'Ř' => 'R',
		'Š' => 'S',
		'Ť' => 'T',
		'Ů' => 'U',
		'Ž' => 'Z',
		'č' => 'c',
		'ď' => 'd',
		'ě' => 'e',
		'ň' => 'n',
		'ř' => 'r',
		'š' => 's',
		'ť' => 't',
		'ů' => 'u',
		'ž' => 'z',

		// Polish
		'Ą' => 'A',
		'Ć' => 'C',
		'Ę' => 'E',
		'Ł' => 'L',
		'Ń' => 'N',
		'Ó' => 'O',
		'Ś' => 'S',
		'Ź' => 'Z',
		'Ż' => 'Z',
		'ą' => 'a',
		'ć' => 'c',
		'ę' => 'e',
		'ł' => 'l',
		'ń' => 'n',
		'ó' => 'o',
		'ś' => 's',
		'ź' => 'z',
		'ż' => 'z',

		// Greek
		'Α' => 'A',
		'Β' => 'B',
		'Γ' => 'G',
		'Δ' => 'D',
		'Ε' => 'E',
		'Ζ' => 'Z',
		'Η' => 'E',
		'Θ' => 'Th',
		'Ι' => 'I',
		'Κ' => 'K',
		'Λ' => 'L',
		'Μ' => 'M',
		'Ν' => 'N',
		'Ξ' => 'X',
		'Ο' => 'O',
		'Π' => 'P',
		'Ρ' => 'R',
		'Σ' => 'S',
		'Τ' => 'T',
		'Υ' => 'Y',
		'Φ' => 'Ph',
		'Χ' => 'Ch',
		'Ψ' => 'Ps',
		'Ω' => 'O',
		'Ϊ' => 'I',
		'Ϋ' => 'Y',
		'ά' => 'a',
		'έ' => 'e',
		'ή' => 'e',
		'ί' => 'i',
		'ΰ' => 'Y',
		'α' => 'a',
		'β' => 'b',
		'γ' => 'g',
		'δ' => 'd',
		'ε' => 'e',
		'ζ' => 'z',
		'η' => 'e',
		'θ' => 'th',
		'ι' => 'i',
		'κ' => 'k',
		'λ' => 'l',
		'μ' => 'm',
		'ν' => 'n',
		'ξ' => 'x',
		'ο' => 'o',
		'π' => 'p',
		'ρ' => 'r',
		'ς' => 's',
		'σ' => 's',
		'τ' => 't',
		'υ' => 'y',
		'φ' => 'ph',
		'χ' => 'ch',
		'ψ' => 'ps',
		'ω' => 'o',
		'ϊ' => 'i',
		'ϋ' => 'y',
		'ό' => 'o',
		'ύ' => 'y',
		'ώ' => 'o',
		'ϐ' => 'b',
		'ϑ' => 'th',
		'ϒ' => 'Y',
		
		/* Arabic */
'أ' => 'a',
'ب' => 'b',
'ت' => 't',
'ث' => 'th',
'ج' => 'g',
'ح' => 'h',
'خ' => 'kh',
'د' => 'd',
'ذ' => 'th',
'ر' => 'r',
'ز' => 'z',
'س' => 's',
'ش' => 'sh',
'ص' => 's',
'ض' => 'd',
'ط' => 't',
'ظ' => 'th',
'ع' => 'aa',
'غ' => 'gh',
'ف' => 'f',
'ق' => 'k',
'ك' => 'k',
'ل' => 'l',
'م' => 'm',
'ن' => 'n',
'ه' => 'h',
'و' => 'o',
'ي' => 'y'
	);
					
	$filename = strtr(html_entity_decode($filename, ENT_QUOTES, 'UTF-8'), $rules);
	return $filename;
}
add_filter('sanitize_file_name', 'my_sanitize_file_name');