I’m about a year into a hopeful polyglot journey, when I started my fourth language, German.
When I started German, I decided to pick back up Japanese rather than let it sit dormant any longer. With Japanese being unused for years, I had lost a lot vocabulary but the grammar was still quite naturally retained. I concur with Dominic about what Olly Richards says about B2 to, but for me, I’ve observed a difference between grammar retention and vocabulary retention.
For about a year, I’ve done something in four languages every day. English is my mother tongue in used in home and professional life. I consume news and personal entertainment mostly in French. I’m also taking French lessons three to five times a week. For Japanese, I mostly engage podcasts and read a little to help with kanji input. I don’t bother any more with an ability to write Japanese, certainly not by hand. With German, I’m taking lessons two or three times a week and work on vocabulary every day and sometimes engage easy podcasts.
I have also developed a system where I have “quick” and “deep” engagement with the languages that are different from each other. Every day, I do “quick” engagement, like back-to-back 10 minutes in each language. I think this helps my brain keep every little language in its tidy little box. For “deep” engagement, here I include structured lessons, watching something on Netflix, reading a book, etc. Sometimes, I even engage my weaker/newer languages through my second language rather than my mother tongue. I love to listen to YouTubers teaching Japanese to French natives where they explain Japanese grammar, vocabulary, idioms, etc. comparatively with French. I think this helps my brain make links that don’t have to channel everything through my mother tongue.
Does it consume time, yes. I do at least ten minutes in every language every day. But it’s a good hobby.
Do I have a problem prioritizing things? Not, really, but this is perhaps in part related to how I differentiate everyday “quick” engagement from not quite as frequent, but more exhaustive “deep” engagement.
Does it get tiring? No, but I don’t think I’ve figured good methods to quickly master the pronunciation of everything.
Is it stressful? No, not at all. I never really confuse things across languages.
Finally, my lifetime goal is five languages. I want to add Spanish in after I get German up to a B1 or so.
Please note though, I don’t really share any of this as “wisdom” per se, as I too am figuring this out. The online apps, sites, tools, creators, and content that make all this possible are revolutionary.