There is great post from Geertjan Wielenga about Translating Oracle JET Applications. If you want to introduce multi language support into JET app - this is great place to start reading from. We are building production Oracle Cloud app with ADF BC REST and JET. This app requires multi language support - English and Lithuanian. I will describe below how we integrated multi language into various areas in the app.
Download or browse through sample application in GitHub repo - JETPlaygroundApp.
In JET we could set default language in index page html root tag. By default it is set to en-US, but it can be set to lt-LT for Lithuanian language or any other language: Read the complete article here.
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