[RPG] Do the exotic languages contain digit characters

There is nothing inherently wrong with sharing secret information; I have done it myself by either sharing notes or talking with individual players in private. I believe it is possible to offer some basic guidelines:

• Share information quickly, a few words at most. Players may lose interest if you spend too much time in secret communication with any one of them.
• For longer correspondences, share the information during a break in play.
• Some information is too trivial to keep secret, particularly when the player will immediately share it with the group. Orcs shouting "Get the Wizard!" likely falls into this category.
• Don't get too carried away with secret sharing. Most of the time its fine to rely on the players to maintain a separation between their knowledge and their character's knowledge.
• If you expect the players to encounter secret information during the game, you can prepare the messages ahead of time. You can use this as a heuristic - if its worth writing out ahead of time, its worth sharing secretly.

Secret information can make the game more immersive and make role playing easier. Ultimately its up to you as the DM to decide what information is worth sharing secretly, and I encourage you to experiment in this area (or talk with your players) to see what feels right.

A background gives you extra languages, on top of the ones you know from your race

As per the basic rules (emphasis mine):

A background gives your character a background feature (a general benefit) and proficiency in two skills, and it might also give you additional languages or proficiency with certain kinds of tools.

When you choose a background, you add the features it grants to your existing traits. Your Outlander Elf should know three languages - common, Elvish, and another of your choice.