First up is the Auri suite of tools, which includes a multilingual AI Keyboard that supports more than 80 languages. It's geared for writing, translation, paraphrasing and grammar checking, but also offers voice dictation and smart notes. Auri is available on iPhone, iPad, Mac and Apple Watch, including free and Pro versions.
Another top contender is Microsoft SwiftKey, which can handle up to five languages and learns your writing style to help you type more efficiently. It's got features like typo correction, customizable toolbars and swipe typing. Microsoft SwiftKey works on Android and iOS devices.
If you're on macOS, Fixkey offers an AI-powered writing assistant that checks grammar in any app without taking you out of the app you're using. It supports more than 200 languages and lets you customize shortcuts, so it can be a good option for writing in multiple languages with a high degree of efficiency.