The special characters tool in VisualEditor makes it easy for users to insert special characters, even if the characters are not present on the users' keyboards.
VisualEditor shares the list of special characters with WikiEditor, the default wikitext editor. This list is shared between all wikis, and you do not need to do anything to enable it on your wiki.
To access it, press the special character button (Ω) to open the tray of characters:
Click on one of the displayed characters to insert it. Click the special character button again to close it.
Adding often-used characters
VisualEditor also lets each wiki's community specify a list of often used characters which will show at the top of the page. This makes it easy for editors to use particular characters that your wiki encourages but that aren't on their keyboards. It looks like this:
To set this up for your wiki, you need create the page
MediaWiki:Visualeditor-quick-access-characters.json. This is a JSON page specifying which characters you wish to show and their sequence. Only
sysop (administrator) users are normally able to create or edit this page, because it is part of the interface. To get an idea of what is possible or useful, you can look at the German Wikipedia's list.
If the text "Often used" appears instead of a localised message, this needs to be translated at TranslateWiki.net; this message is the "