And that result is here already. During my Japanese lesson today, I had a harder time overall getting words to come out, and noticed a few distinct thoughts in French while I was trying.
Have others here experienced this too? Did it pass quickly or were you stuck with it for a long time? Did you do anything in particular which helped?
This is one reason I havenāt tried picking up an āeasierā language like French, Spanish, etc. that I previously āstudiedā at school, despite them being useful back home. Iād also be interested in hearing peopleās experience with learning multiple languages.
I havenāt actually had to speak in any language other than English or Japanese, so Iām not sure.
Going off of a complete guess, I think itās probably like the normal problem of switching from your native language to something else, except now you have an extra language floating around. You understand the context of the speech and the words contained, but your response is independent of the language of the conversation because French and Japanese contexts havenāt been fully established in your brain (itās just ānot Englishā)ā¦ or something like that.
I imagine itās just a matter of practicing with both.
Right, I think when I hear something in French or Japanese, my brain processes the meaning and files it under ānot Englishā.
I had French conversation lessons a few years back, but Iād pretty much lost the ability before I started outputting Japanese this year. Iāve been listening to enough French to keep my comprehension level up fairly well, and my Japanese comprehension still has quite a way to go to catch up with it. When I was just listening to French, that didnāt interfere with my Japanese, but trying to speak French again did.
Yeah, Iām currently taking French classes and it does sometimes get a bit mixed up with Japanese. I find mostly itās an issue if Iāve been working with the other language previously and Iām trying to ssy something off the cuff ā it seems to take a little while for my brain to get into the right āmodeā. By 10 minutes into a lesson itās fine, and for comprehension rather than production Iāve never had a problem, with the exception that for listening exercises where youāre listening for a number Iāve once or twice heard ācinqā and thought āććā => āthreeāā¦
I learned both French and Dutch as a child, but at the time they didnāt interfere with each other. I think that context differences helped with that: I learned French in school, and I learned Dutch from my grandparents.
These days reading is the only French skill Iāve kept up. (Iām a Canadian web developer, so I deal with bilingual websites.) My husband, though, likes to ask a french translation of a random word on occasion. In those cases, Iāve noticed that if I know the Japanese word, itāll pop into my head first.
I think it might be mostly about what language youāre most used to in relation to a certain field at the current time. Itās not rare for me to think about Japanese or English equivalents first even in context of my native language.
I think thatās only a small part of it for me, but it does happen. I was doing OK in a French lesson until the teacher asked me about what anime Iād been watching recently, and then my brain froze trying to answer that 
It seems to be getting better. And for now, Iām taking more time to prime my brain with the right language before a lesson or other call. In the evening the day before a call, Iām focussing mainly on the relevant language, then Iām making sure that language is the last one I focus on right before I need to use it. So if I have a French lesson coming up: focus on French the evening before; then on the day, do my Japanese Anki reviews first thing, and listen to something in French after Iām done with those.