On the Translations page, an "Add a Language" field opens the editor on
a new code starting from English — every key with its English text and
an empty field to translate — and a "Copy English" button seeds the
blank cells as a starting point. Saving writes config/lang/<code>.ini,
so a new language no longer means download-rename-upload.
Front-end only: the translation_keys ajax already returns English and
whatever a code translates for any valid code, and translation_save
writes the custom file (PR #364). The controls reuse the editor's
load()/save path; no controller or store change.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
