Manual:$wgCategoryCollation

The setting determines what collation^[1] algorithm should be used to sort category listings.

As an example, to use the Spanish collation, you'd write $wgCategoryCollation = 'uca-es'; in LocalSettings.php and then run updateCollation.php for your change to take effect.

Currently supported are:

Since MediaWiki 1.18, extensions can add extra collations via the Collation::factory hook.

The value is also stored inside the categorylinks table to determine which rows need updating when the collation algorithm changes.

MediaWiki also supports many collations designed for specific languages. These are based on the Unicode collation algorithm (UCA) uca-default and have the same requirements; they are named uca-<langcode>, where <langcode> is one of:

af, am, ar, as, ast, az, be, be-tarask, bg, bn, bn@collation=traditional, bo, br, bs, bs-Cyrl, ca, chr, co, cs, cy, da, de, de-AT@collation=phonebook, dsb, ee, el, en, eo, es, et, eu, fa, fi, fil, fo, fr, fr-CA, fur, fy, ga, gd, gl, gu, ha, haw, he, hi, hr, hsb, hu, hy, id, ig, is, it, ka, kk, kl, km, kn, kok, ku, ky, la, lb, lkt, ln, lo, lt, lv, mk, ml, mn, mo, mr, ms, mt, nb, ne, nl, nn, no, oc, om, or, pa, pl, pt, rm, ro, ru, rup, sco, se, si, sk, sl, smn, sq, sr, sr-Latn, sv, sv@collation=standard, sw, ta, te, th, tk, tl, to, tr, tt, uk, uz, vi, vo, yi, yo, zu

For example, to use a collation for Spanish, one would use the uca-es collation.

Using these collations provides both correct sorting order for given language and proper headings for first letters of article titles. Earlier versions of MediaWiki might not support all of these language codes.

There are two parts to having a new language supported:

• It being supported by the International Components for Unicode library (the list of language codes it supports is available at [1]). Note, however, that Wikimedia's production servers do not use the latest version of the ICU library. As of 2016, they use version 52.1, which supports a significantly smaller set of languages.
• It being additionally supported by MediaWiki itself (this basically requires listing the additional characters, or character groups, that are considered separate letters in the given language, in addition to the basic alphabet) – the always up-to-date list of currently supported ones is available at includes/collation/IcuCollation.php.

It might also be the case that the default ICU ordering ('uca-default' collation) orders the titles correctly, but does not correctly separate the letters – it can be used for the first step in that case. Sometimes the letter ordering of a different language might fit yours, if they are related – a custom collation can sometimes be provided in such case (there is one for Sorani Kurdish / Central Kurdish language ('ckb') already, called xx-uca-ckb includes/collation/Collation.php).

Under numeric sorting, pages will be sorted as such: 1, 2, 9, 10, 11, 20, 21, 99, 100. Under regular (non-numeric) sorting, pages will be sorted as text: 1, 10, 100, 11, 2, 20, 21, 9, 99. If numeric sorting is used, all pages starting with a number will be sorted together under a single header: "0–9". If regular sorting is used, pages starting with a number will be sorted under separate headers for whichever number each title begins with: "0", "1", "2", etc. For more information about numeric sorting, see the Unicode Technical Standard #10. To test numeric sorting, see the ICU Collation Demo. Note that numeric sorting only works for unbroken sequences of digits. Digits separated by commas, periods, or spaces are treated as separate numbers.

• MediaWiki 1.17/Category sorting - release notes about this feature from MediaWiki 1.17.

• ICU Collation Demo