i18n Fallback languages

The TEI-Publisher supports many languages but not all are translated 100%. Compare: https://crwd.in/tei-publisher. If a label is not available in one language, the fallback language for the label is: English.

Feature Request: make the fallback language configurable out of all languages that are 100% translated. In best case users can decide themselves which of the supported fallback languages to use when their default language does not cover 100% of TEI-Publisher labels.