How to compare Unicode strings in Javascript?

Here is an example for the french alphabet that could help you for a custom sort:

var alpha = function(alphabet, dir, caseSensitive){
  return function(a, b){
    var pos = 0,
      min = Math.min(a.length, b.length);
    dir = dir || 1;
    caseSensitive = caseSensitive || false;
    if(!caseSensitive){
      a = a.toLowerCase();
      b = b.toLowerCase();
    }
    while(a.charAt(pos) === b.charAt(pos) && pos < min){ pos++; }
    return alphabet.indexOf(a.charAt(pos)) > alphabet.indexOf(b.charAt(pos)) ?
      dir:-dir;
  };
};

To use it on an array of strings a:

a.sort(
  alpha('ABCDEFGHIJKLMNOPQRSTUVWXYZaàâäbcçdeéèêëfghiïîjklmnñoôöpqrstuûüvwxyÿz')
);

Add 1 or -1 as the second parameter of alpha() to sort ascending or descending.
Add true as the 3rd parameter to sort case sensitive.

You may need to add numbers and special chars to the alphabet list

You may be able to build your own sorting function using localeCompare() that - at least according to the MDC article on the topic - should sort things correctly.

If that doesn't work out, here is an interesting SO question where the OP employs string replacement to build a "brute-force" sorting mechanism.

Also in that question, the OP shows how to build a custom textExtract function for the jQuery tablesorter plugin that does locale-aware sorting - maybe also worth a look.

Edit: As a totally far-out idea - I have no idea whether this is feasible at all, especially because of performance concerns - if you are working with PHP/mySQL on the back-end anyway, I would like to mention the possibility of sending an Ajax query to a mySQL instance to have it sorted there. mySQL is great at sorting locale aware data, because you can force sorting operations into a specific collation using e.g. ORDER BY xyz COLLATE utf8_polish_ci, COLLATE utf8_german_ci.... those collations would take care of all sorting woes at once.

Mic's code improved for non-mentioned chars:

var alpha = function(alphabet, dir, caseSensitive){
  dir = dir || 1;
  function compareLetters(a, b) {
    var ia = alphabet.indexOf(a);
    var ib = alphabet.indexOf(b);
    if(ia === -1 || ib === -1) {
      if(ib !== -1)
        return a > 'a';
      if(ia !== -1)
        return 'a' > b;
      return a > b;
    }
    return ia > ib;
  }
  return function(a, b){
    var pos = 0;
    var min = Math.min(a.length, b.length);
    caseSensitive = caseSensitive || false;
    if(!caseSensitive){
      a = a.toLowerCase();
      b = b.toLowerCase();
    }
    while(a.charAt(pos) === b.charAt(pos) && pos < min){ pos++; }
    return compareLetters(a.charAt(pos), b.charAt(pos)) ? dir:-dir;
  };
};

function assert(bCondition, sErrorMessage) {
      if (!bCondition) {
          throw new Error(sErrorMessage);
      }
}

assert(alpha("bac")("a", "b") === 1, "b is first than a");
assert(alpha("abc")("ac", "a") === 1, "shorter string is first than longer string");
assert(alpha("abc")("1abc", "0abc") === 1, "non-mentioned chars are compared as normal");
assert(alpha("abc")("0abc", "1abc") === -1, "non-mentioned chars are compared as normal [2]");
assert(alpha("abc")("0abc", "bbc") === -1, "non-mentioned chars are compared with mentioned chars in special way");
assert(alpha("abc")("zabc", "abc") === 1, "non-mentioned chars are compared with mentioned chars in special way [2]");

You have to keep two sortkey strings. One is for primary order, where German ä=a (primary a->a) and French é=e (primary sortkey e->e) and one for secondary order, where ä comes after a (translating a->azzzz in secondary key) or é comes after e (secondary key e->ezzzz). Especially in Czech some letters are variations of a letter (áéí…) whereas others stand in their full right in the list (ABCČD…GHChI…RŘSŠT…). Plus the problem to consider digraphs a single letters (primary ch->hzzzz). No trivial problem, and there should be a solution within JS.

Funny, I have to think about that problem and finished searching here, because it came in mind, that I can use my own javascript module. I wrote a module to generate a clean URL, therefor I have to translitate the input string... (http://pid.github.io/speakingurl/)

var mySlug = require('speakingurl').createSlug({
    maintainCase: true,
    separator: " "
});

var input = "Schöner Titel läßt grüßen!? Bel été !";
var result;

slug = mySlug(input);
console.log(result); // Output: "Schoener Titel laesst gruessen bel ete"

Now you can sort with this results. You can ex. store the original titel in the field "title" and the field for sorting in "title_sort" with the result of mySlug.