[wudangmonk]

I really can't relate to most of your points. Words either come naturally as they do for everyone else or you don't use the word in that language therefore you will try to guess it or think of a similar one. This just means that you are not exposed to the same vocabulary in both languages. All my Comp Sci and Math vocabulary is in English because of school/online/talking to others. All my botany and plant knowledge knowledge is in Spanish because its my mother's hobby and that's how I know it. Only if I switch the languages will I struggle with the vocabulary.

The only time when I felt having to use more mental capacity was when I wasn't fluent in the language, the idea of languages being a constant cognitive load is as ridiculous as thinking that you are better off not knowing anything at all due to the toll knowledge takes on your mental capacity.

[notdang]

Don't know how ridiculous it is, but I live in a Spanish speaking country, using English at work, consuming English part of the internet, occasionally using Russian during the day (because of Russian "refugees") and no one around me speaks my native language. There is a cognitive load.

[lIl-IIIl]

I would think that the cognitive load is there because you are speaking a foreign language (whether one or many). I don't think it's debatable that speaking a foreign language day in day out with no one to speak your native language can wear you out.

[IIAOPSW]

I don't see why its ridiculous. Brains are not magically above the constraints of information lookup from a database. The more you know, the more you have to sort through somehow.

[watwut]

That is not how it works? People who know a lot are not in general slower then people who know only a little.

[IIAOPSW]

Have you tested that or are you conjecturing from intuition?

[watwut]

Did you tested it and found people who know a lot to be slower in answering questions then those who know only a little?

Depending on how you define tested, yep, people who I know that know a lot are not slower answering questions that know only very little.

[nohaydeprobleme]

I also don't experience the extra cognitive load of choosing between languages when trying to express ideas, unless I'm trying to learn a new vocabulary word that I'm not familiar with. In specific, I can't relate to the commenter's point that: "When trying to think of a word, it comes to you in four different languages, which isn't helpful!"

As objective evidence, I use a software app called Glossika to practice listening and speaking to some extent, where the software plays a spoken English audio phrase and pauses before playing the translated audio. When I see the English for the phrase "The computer crashed" in Spanish track, the Spanish equivalent only comes to mind, and I don't simultaneously think of the French translation—even though I'm later asked to translate the same English phrase in the French track. At the start of each track, I have a certain context in mind (to make responses in a particular language), so I don't personally struggle with having to consciously focus to avoid mixing up words. In my experience, after at most ~20 seconds or so working in the target language, I say the right translations without any extra conscious effort of avoiding the usage of the wrong language.

The same goes for conversation practice. At the very worst—sometimes at the very start of a conversation—I can mix up a basic word. But after about less than a minute or so of speech, I'm think and express only in the language I'm practicing; I don't continually struggle with interference with other languages.

For my personal experience, studying both French and Spanish has even been beneficial for vocabulary acquisition. Learning that "le public" means audience in French made it a lot easier to shortly after remember that "el público" also means audience in Spanish. The sounds in French and Spanish are different, along with the words that typically surround new vocabulary words, so I don't personally struggle with choosing between different word options from different languages.

Speaking French and Spanish also has a separation due to the way that pronunciation physically feels. The back-of-the-throat guttural R in French especially feels and sounds a lot different than the Spanish trilled R with a vibrating tongue near the front teeth—so there is a barrier to mixing up French and Spanish words with these different sounds, as they "feel" very different to say in the mouth and throat. Spanish words also have a "stress" on the second-last syllable or syllable with a certain accent (e.g. Le envió for "I sent it to you" with a stress on the accented ió), whereas French has roughly equal stresses as a "syllable-timed" language [1], so the feelings of speaking the languages are very different, even if the vocabulary can be similar at a first glance.

In summary, I just can't relate at all to the idea of "juggling" between languages from practice with audio programs and conversation practice each week, though I recognize that different people have different experiences.

[1] https://ielanguages.com/french-stress.html