Why isn´t there an achievement for full alpha imperial?

There is, it's separated though.
Here.

what do you mean ... separated?

and why don´t i get it?

i own full alpha imperial, check my active inventory

By separated, I mean it's not next to the "Full 'x'" achievements.
And perhaps it's bugged; might appear in a couple of minutes I suppose.

If not create a thread on the support section or join #support.

Ok thanks for the quick answer, i appreciate it

Updates occur every 24 hours, so I would wait about a day if you haven't already.