Sorry, i'm not good at english.
If your Lightroom is Creative Cloud, you can change the language.
Step1. Change language setting in Creative Cloud Desktop Application.
Adjust the install language | CCM
アプリケーションの言語を指定してインストールする方法(Creative Cloud)
※Please see screenshot.
Step2. Delete Lightroom.
Step3. Reinstall Lightroom from Creative Cloud Desktop Application.