Previously using a SwiftKey Account:
If you were previously using a SwiftKey Account, just sign in to your SwiftKey Account after upgrading and all your learned language (from the beta and/or your market release SwiftKey) will be combined and saved into your SwiftKey Account.
Not previously using a SwiftKey Account:
Upgrading to the latest market version of SwiftKey for Android should not affect your learned language.
If you decide to create a SwiftKey Account, all of your learned language will be saved to your SwiftKey Account and from then on you should never lose your language again. See the article, ‘What is the SwiftKey Account?’ for further information.