Check CLI text translation state and consider enabling translations when headless

**What is the current behaviour and why should it be changed?**

The client and server code behave differently on start up when headless, in regards to loading translations.

Ideally both would load translations once the application instance had been created and all text displayed - either in the GUI or to the console - would be translatable.

**Describe possible approaches**

* Review existing code to identify any text that _should be_ translated that _is not_.
* Review existing code to identify any text that _should not be_ translated that _is_.
* Raise a PR to resolve the above.
* Once that's done, review the start up code in `src/main.cpp` to ensure translations are loaded as soon as the run time language has been established. Currently, this _**must**_ be after command line and settings processing as both can affect the language selection.

**Has this feature been discussed and generally agreed?**

Mentioned, possibly several times, previously. Most recently in #3139.

Review the existing client and server startup and text-handling code, using the discussion in #3139 as context. Check which displayed strings should or should not be translated, then inspect src/main.cpp to trace command-line and settings processing. Done means the translation policy is consistent and translations load after the runtime language has been established.

Written by the indexing model from the issue text.