The following note, added together with 6.2.9 / MGNLREST-286 is misleading:

When configuring the property for a multi field, make sure it is defined at the level of the field itself (not its child entries).

It has the following effect, which may or may not be what a customer wants:

Setting i18n to true on a MultiField means that you want to store a different set of entries per locale.

—via SUPPORT-13105

1. To translate a unique set of entries: set i18n to false on the multi-field, and set i18n to true on the inner field.
2. To translate different sets of entries, set i18n to true on the multi-field, and set i18n to false on the inner field. In this case, there is no fallback between languages.
3. Setting i18n to true on both levels should be discouraged (no benefit afaict, enquired on the SUPPORT ticket tho).

Both options work equally with REST Delivery.

And since this has been source of confusion forever (including in UI 5), that probably deserves a separate section, showing the different JCR structures?