In T135092#2312662, @jeblad wrote:

No, this is not a good solution. I have set up an example, but it is way to cumbersome. The real solution is to add an updated input method.

I'm not clear what you mean; could you specify?

1. We encourage people to use an input method editor (i.e., a piece of software on their computer) that 'corrects' what they type by getting in the way of their typing as they go, prompting them to change typed "s into a « or a ». Does such an input method exist already?
2. We write and force people to use a new input method editor that we write inside UniversalLanguageSelector that 'corrects' what they type by getting in the way of their typing as they go, prompting them to change typed "s into a « or a ».
3. Whenever anyone writes a " in either the wikitext or visual editors, it is transformed on save by MediaWiki into a « or a ». This is used by a few languages, normally for ae -> æ and similar transformations, but is pretty aggressive and it makes it impossible to e.g. write articles about punctuation as these characters won't be shown.
4. Whenever anyone writes a " in the visual editor, it is transformed as they type by some code into a « or a ». If this is what you're asking for, the answer is probably 'no' due to the performance issues; we don't do language-specific hacks in the editor, but such a tool could be written as a gadget (though it'd be quite irritating for users, so I'd caution against it without some serious research on the impact on e.g. how much new users find it disruptive).
5. A bot goes around correcting these minor annoyances.
6. Something else.