When creating a new wiki article, it's not possible to use the following characters: \ / : * ? " < > | [ ] ^ +
This restricts common delimiters like colons or question marks. For example titles that are written as question ("Wikis: What is a good title?"). Here we have two forbidden chars at once (?:). Quotation marks can be used for error messages: How to fix "404 file not found" error
I see only one reason to disallow such characters: For the human readable URL title of the article. But this can be easily fixed by replacing all special characters to some non problematical ones. I personally did this in ASP.NET Core projects: Simply allow [A-Za-z0-9] and novate anything other by dashes (-).
You can find sample snippets here: https://stackoverflow.com/questions/37809/how-do-i-generate-a-friendly-url-in-c
This is C# but can be easily converted to Java for integration in IBM Connections.
Recently I noticed that we already have this feature in the blog module: I copied all the special characters from above in the title without any error message. This isn't good for users since they use such chars in blogs and got confused because they can't do so in wikis. But it also means that you already have the described logic implemented and can re-use them in wikis, too.
Or even better: Do some refactoring and arite a shared module that checks/handles ALL titles. This ensures a consistent behavior across all your modules. And it also make your live easier cause Connections get maintainced more easily.