i18n: Spoken languages are not translatable

[tristanlabelle]

For example:

They come from a database that contains English strings:

@functools.cache
def get_language_dict() -> dict[str, str]:
    """
    Get a list of allowed languages as a dictionary of {code: name}.
    """
    with session_scope() as session:
        return {language.code: language.name for language in session.execute(select(Language)).scalars().all()}

[tristanlabelle]

The frontend has localized mapping from language codes to language names which we can use if the language codes match (2 vs 3 char codes?)