You can really use any library you want, as long as your library consumes JSON. In the end, i18nexus is a platform that simply generates JSON files of key value pairs. Our software does have features specific to i18next such as syntax highlighting for pluralization, contexts, and interpolators, but if you don’t need this fancy stuff, you can simply use any syntax you want.
Machine translating isn’t quite “unlimited”, but it’s close. You have a set number of machine translated characters per month, however, we give you such a high limit that it will be difficult for your team to exceed the limit. We use Google Translate and DeepL for our machine translations and these services aren’t free. If you do for some reason reach the limit, contact us and we can work something out for you.
Nope, i18next is open source. There are maintainers of the library, but we are not associated in any way. We are simply a platform for managing your translations and easing your integration.
Your plan is set at the Team level, not per project. Besides user limits, the only thing that plans are limited to are strings. So if you have a 10,000 string limit on your plan, you can spread out these 10,000 strings amongst as many projects and languages as you want on your team.