In WordPress the typical architecture we see is the single site instance. But WordPress has an underlying architecture that supports Multisite instance - unlimited (?) websites under the same WordPress installation. Typically, for bi-lingual WordPress sites, it's the best architecture to use Multisite.
Multisite as Multilingual
With multisite, both the sites are detached, but they are in the same WordPress installation. That means you don't have to maintain two (or more) different WordPress installation, but you can maintain them like separate installation. So plugins like Multilingualpress will help you to bind the contents while managing content in all the different languages.1
With multisite and multilingualpress, you can manage sites like below:
Single Site as Multilingual
But as you want to maintain multilanguages in multisites. You can use Multisite architecture with Polylang plugin. Polylang enables you to have multilingual in single site instance. It's not recommended, and not a good architecture, but sometimes it's better to get bi-lingual site in single site instance instead of a huge multisite architecture. With polylang, content management could be a bit messy, because contents for both (or all) the languages are in the same place.
With Multisite you can have your branch and parent company website:
example.com/ (parent site)
- example.com/ (default lang)
- example.com/lang2 (secondary lang)
example.com/branch (branch site)
- example.com/branch/ (default lang)
- example.com/branch/lang2 (secondary lang)
Both the Polylang and MultilingualPress has their own Pros and Cons. So you have to test them thoroughly in test environment to ensure them to function as you want, or at least you can bring comfort to what they are providing.
1. Multilingualpress for Gutenberg editor is a paid service now. If you use Classic editor, you can use Multilingualpress free version