Learn a another human language. You don’t have to be good at it or even able to converse. Languages are systems of thinking as much as they are systems of communication. Some thoughts only make sense in a given language! The process of learning a language builds cognitive skills and perhaps fights cognitive decline. If you have absolutely no “ear” for human language start with Esperanto and work your way to additiona…
I would perhaps recommend Latin, because it has a huge and rich literature, and uses essentially the same script as English.
To learn a language effectively it's important to be able to immerse yourself in it. Youtube with auto transcripts, Netflix w/ subtitles, news in written form, chatting with native speakers in a language exchange by texting or skype, tutoring, etc. Once your reach A1-A2 level by any traditional mean, you will have a lot of options to get to fluency.