Clarify behavior when not creating a FT index but still passing titles

[benoit74]

I'm a bit embarrassed regarding Creator configIndexing() method.

This is current documentation:

To me, it implies that:

• it is not possible to disable title (suggestion) index
• title index continues to work when .configIndexing(False, "en") (for instance) is called
• the same language is used for full-text and title indexes

But documentation is not really clear on that, and I do find only one test in libzim with FT disabled, so it feels like this area probably deserves some clarification.

It is a bit unclear as well what happens when we pass an empty string as language. I find no test as well. Do we fallback to "original" logic when no language is configured for stemming?

[kelson42]

Is it clear what is the string representation of the language? Which norm is expected here?