How to Detect when user re-opens the Application

I already posted a problem I have regarding the UI and Custom Fonts on:

A solution would be for me to force a locale change of the application, already tested.

Problem is that I would need to know when the user opens the application again, meaning, the app that was stored in the cache.

My UI problem is cache related, it seems to happen always when a user re-opens with data in the cache.

So, is there a way to find out when the user opens the Application that is not the first time ?