Lit-localize cannot be used by more than a single script on a website, meaning we can't use it in plugins and can't use it to translate text within components.
After dabbling a bit it looks like i18next does not indeed come with XLIFF support built in. I therefore suggest - for the time being - to stick with lit-translate for translating individual plugins.
Lit-localize cannot be used by more than a single script on a website, meaning we can't use it in plugins and can't use it to translate text within components.
According to a helpful comment in the as yet unsolved issue #1661 on lit/lit a workaround that has been used in production for a while is https://github.com/weavedev/lit-i18next. The package consists in a trivially thin wrapper around the stable industrial strength i18next library, which comes with our much sought-after
XLIFF
support as a matter of course. Maybe we could investigate switching to that as a translation mechanism.