Note: You are currently viewing documentation for Moodle 3.2. Up-to-date documentation for the latest stable version of Moodle is probably available here: Unicode.
Unicode is a character set that allows one to support practically any language and many special characters used in science, math and technology. Moodle transformed (optionally in 1.6 and 1.7, required in 1.8 on) to Unicode to better be able to support different languages.
In MySQL, the database collation has to be set to unicode before the Moodle database is created. There are two different Unicode collations used: utf8_general_ci (default) and utf8_unicode_ci. The utf8_general_ci collation is slightly faster but less accurate than the utf8_unicode_ci collation in representing all the characters in languages. For this reason, Moodle tables are normally set-up using the utf8_unicode_ci collation. For a discussion of the difference between the collations see the MySQL documentation.
Free On-line Unicode Character Map gives you the possibility to see the different characters that are supported (or NOT!) in your browser and see which code is used if you need that. A nice feature with the characters is that you can easily enlarge the text in your browser to see them better. ([Ctrl]+[+] in Mozilla) If you are interested in Math symbols check list "22 Mathematical Operators". For Chemists looking for arrows, list "21" might be interesting.
Moodle has good support for mathematical expressions in its TeX filter, but using Unicode instead can sometimes be good. In some places (i.e. CLOZE questions) the \ characters for TeX can cause problems, whereas Unicode characters won't. A user can enlarge an expression with Unicode.