i18n server and client side

### Background Information
We need to have i18n for every user-facing text.

### What
Client-side needs to have i18n and server-side responses that contain text needs to have i18n as well.

For the server-side, we don't care about logged messages and content translation, just messages that are sent to the user.

### Acceptance Criteria
- [x] Apply i18next in the front-end
- [ ] #460
- [ ] Apply i18next in the back-end