Translate to content language

Synopsis

When the content and the interface languages are different, Drupal core doesn't provide a way to translate fixed strings to the content language. To help modules and templates both, this module:

• automatically changes the t and trans filters and the % trans % tag in the templates under the default theme directory to use the content language as default instead of the interface language.
• Adds the tc function
• Adds the TrancTranslationManager::CONTENT_LANGCODE constant, usable in any t / format_plural / new TranslatableMarkup / string_translation service calls.
• Adds new twig filters: tc / transc translates to the content language in any theme, ti / transi translates to the interface language in any theme.

Also, config objects -- webforms, views -- do not work properly in this scenario. The tranc_config submodule is provided for this purpose.

Known problems

• There is no way to force the % trans % tag to translate to the interface language in the default theme as it is unlikely the shorter strings of interface would require this tag.
• In a template not under the default theme, translating to the content language with the % trans % tag requires the constant() Twig function. This has not been tested.