For reference languages are chosen only translated languages.

Related: forge.typo3.org/issues/65631

EN doesn't need to be specified in configuration as viewed language.

Using english as default language on editFile page if default typo3 language is empty.
This allows that editFile page content is shown in case when english is not default language in typo3 instance, but it has language constants and there are no constants in the default language of typo3 instance.

Adds checkbox to backend user settings which allows to non-admin users to switch between editing modes.

There is no error possibility if XLF body tag is empty.
Exception appears only if there is no body tag at all in the xlf file.

Also, fluid code is refactored.

Not throwing exception if main language file has no constants and en is not default language in TYPO3

Solves problem with TYPO3 having default language which is not english, and english is default language in all localization files.

Fixes: #65530

Also fixing description output.

- Configuration
- Editing modes
- Insertion modes
- Known Problems And Hints
- Manage Backups
- Search Constant
- View Tree

Not using first person.

- Introduction
- General
- Edit file
- Edit constant
- Add constant
- Delete constant
- Rename constant