my languages tend to get quite mixed up
i’m fluent at (near) native level in english, german, swissgerman and french. (near native because i somehow just can’t flirt in french, it’s weird). i’ve also got some latin and italian, can understand a spanish tv-show if i’m paying attention, can read dutch somehow. but i use the first four daily. i usually stick to one language in a specific interaction, but if i’m searching for a word my brain often offers up the same word in a different language. i have no idea how to stop this.
when i’m talking with my family (or other groups of multilingual people), who share the same languages, things sometimes get weird: the conversation veers wildly between languages, words are mixed in all the time, sometimes an entire sentence will be spoken with the vocabulary of one language, but the grammar of another. sometimes there will be a major conversation in one language, and a minor side-conversation in another.
it can be a problem when speaking with somebody who only shares one language, but my brain tends to focus down a bit in those situations. and when words or grammar from a different language does slip in then i notice quickly and can correct myself.
and that kind of reflects my attitude to language learning: i will never sound like a native, these days i have a vague “foreign” accent even in my mother tongues. i will always make slight mistakes because when i relax my brain mixes languages. but that’s okay: languages are not rigid cages defining how we are allowed to speak. they are wonderfully flexible tools which allow ourselves to express ourselves.
as for japanese, so far it’s not been much of an issue, and i don’t know why. i have found myself adding a quick ね at the end of a sentence, but not much else. probably it’s because i just haven’t had the chance to actually speak japanese yet. but that said, my internal monologue is just starting to integrate bits of japanese.