English is the accepted language in all language-related SE sites.
In each language-related SE site, its own language scope is the preferred one (for example Spanish in Spanish SE site, French in French SE site, etc.)
But just these two languages (English and the language of each language-related site) are accepted for askers.
I want to ask to add all languages so that every person can ask.
Surely, there are many people on the world who are eager to learn a language. Perhaps a Turkish man that doesn't know English wants to learn French. But because of SE policies, he can't ask his questions in Turkish language in French SE site.
He can ask, then a Turkish person who also is in the French SE site answers him in Turkish.
May you say there's Google Translate too. But note that Google Translate is so weak and incomplete for some languages because its citizens haven't contribute in them as well.
If this feature is enabled, I think the language-related sites will get more contributions and views.