Firstly, I agree with what Luciano has mentioned. If the users don't have any choice, why make it seem like there is one? It's like advertising great offers that aren't in stock.
However, if what you want to do is communicate that the feature is in progress then...
Firstly I would ask you, how soon can you realistically deliver the other languages? If you can deliver them in a relatively short time then it might be acceptable that you display in "in progress" languages within the menu including a short text stating that you're working on it.
For example your menu might look like this:
*Spanish (Disponible pronto)*
*French (Bientôt disponible)*
With the "available soon" options grayed out.
I would only suggest this if your users are anticipating the feature already, from client-company rapport and feature requests, then it would be beneficial to provide a reassuring message that the feature is under development.