Will upgrading SwiftKey lose my personal/learned language data?

No, it shouldn’t.

Your pesonal language profile is stored on your SIM card. On installing SwiftKey, learned data from the trial version is inherited. Uninstalling SwiftKey can clear your learned language data, so if you are upgrading from trial to the full version of SwiftKey it's best to install the upgrade before uninstalling your previous version of the app.

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