English (UK): "idea" becomes "idaea", names lowercase in suggestions

Steps to reproduce

1. Use English (UK) as the keyboard language.
2. Type "good idea" and press space, or swipe "idea", or type "what a good" and look at the prediction.

What I expected

"idea" stays "idea" and is offered in predictions.

What happened instead

• Typed "idea" is replaced by "idaea" after space; swipe gives "idaea"; predictions offer "idaea".
• The same happens to a few other words: seed → saeed, med → moed, composite → compositae, maize → maise, Eric → Aeric, Romania → Roumania.
• Names, days and months (London, English, British, Monday, Christmas, Michael…) are completed in lowercase and ranked very low ("Lond" → london).

Also in English (Australia) and English (Canada): "english", "christmas" in lowercase when completing after some context.

Found internally while adding English (Australia) and English (Canada) (#S487).