Localization is not working in welcome screen

Hi Team,
We are upgrading from 3.4.3.final version to 10.0.2 version. We have customized admin, login, and account modules by overriding a few js and CSS files and mentioning the same in themes.properties of each individual module.

We are supporting English, Japanese and French languages. When we select any language in the login screen we are able to see the localization as oper the selection but once we login successfully we are not seeing localization in the welcome screen, every time it is showing a screen with English though we have selected ja or fr language in the login screen.
Could someone help me with this, Thanks in advance.

Can anyone help me with this, We have upgrade to 11.0.1 from 3.4.1 but we are blocked with a Localization problem. Why admin module not picking up the localization value every time locale value is setting to ‘en’. We have to support Japanese and French languages as well.