First, setup up your most used signature (and most used title) as the default signature. You can create your signature by going to Tools\Options and then clicking the Mail Format tab. Click the Signature button near the bottom and you'll be presented with a dialog window where you can create new signatures. Create one now and it will become your main (or default signature).
2
Then create another signature (e.g., with a different title) and save it under a different signature name. For example, if your default is "User English," then call your alternative something like "User Spanish."
3
Now when you start a new email, your default signature will appear in the email window. To use your alternate signature, right-click over the signature and you will see a pop-up menu with the two signature choices. Choose "User Spanish" and you'll see your alternate signature replace the default one. You can create multiple (more than two) signatures if you wish.