4 years ago only WPMl was the solution to a multi-language site that supports custom fields (as our themes do). But unfortunately WPML is a difficult plugin to manage and use since it requires translating EVERYTHING manually.
We had the chance to test other multilanguage alternatives, still 3rd party plugins, but much easier to handle.
Weglot is really easy to work with, doesn’t need to translate anything besides the labels and shows all bookings/properties in all languages without any hassle.
You login and you can modify wrong translations as explained in their official wordpress plugin description
You get a free test account on registration and it’s easy to setup and test for yourself. This one we had the chance to test ourselves and was really easy to use.
Another client recommended https://gtranslate.io/ We didn’t have the chance to test this one ourselves, but seems to be the same as Weglot at a cheaper version.