Fix: Possible double free when resetting PGS subtitles.

This resulted in random crashes when seeking quickly in a file with PGS subtitles and other various cases.

Fixes #4240.
Update translations from Transifex:

 - Catalan
 - Croatian
 - Japanese
 - Slovenian
 - Spanish

Fixes #4268.
Translations: Move the language resources to their own file.
Move the UI language selection to the option dialog.

The growing number of translations makes the menu difficult to use.
UI language: Remove the resource IDs.

We don't need resource IDs anymore except to maintain compatibility with the language setting saved from really old versions (nearly two years old). The compatibility gain isn't worth the trouble so people upgrading from those old versions will now have the UI language reset to the default language based on Windows localization.
Subresync bar: Use translatable strings when possible.
Capture dialog: Split some functions and factorize some code.
Fix: The dockable bars were not updated when changing the UI language.
Use the event system to handle UI language changes.