Cannot select specific sprites in sheets

I tried to follow the practice of using "power of 2" textures, and this led me into having unrelated images in the same sheets for the sake of saving memory.
But now that I am attempting to use the localization package on top of my project, I am having a huge issue : whenever I select a sprite, the whole sheet is selected and appears in the table. And when the game runs, the "first" sprite of the sheet is always the one being displayed.

The problem is that I have my various translations in different places of the sheet.
What's especially weird is that when I select my sprite, I can actually pick the sprite I want instead of the sheet, and unity displays me that sprite for a moment. But it's gone as soon as I edit anothert sprite in the table.

Is that a bug? If not, how can I choose a specific sprite in the sheet as my translation?

Thank you.

 

OK. I am willing to do it but how does that work exactly? Is it a form? A specific part of these forums?

Also, do you want me to take screenshots to illustrate the problem more clearly? Or is the memory/file transfer aspect a problem?

 

I am still having the same issue in 1.3.2. Only the first sprite in the sprite sheet is being used.