What studies, if any, address the study of multiple related languages (as in a relatively high level of mutual intelligibility--Spanish, Portuguese, Italian & French; Dutch & German, etc) simultaneously, by adult learners?

Does this provide a synergy for the student, as many concepts are similar across the languages, or does it provide confusion, as the languages may have too much overlap to be kept distinct in the student's mind?

Or are there other, less intuitive, differences (benefits or drawbacks)?

For the purpose of this question, note I'm not interested in the general study of multiple languages, but specifically those which are similar.

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    @erip: From an SLA standpoint, being in the same language family is not always very meaningful. English and German are both Germanic languages, but are not very similar. Dutch and German are quite similar (a high level of mutual intelligibility). If a more precise definition is needed for my question, I'm willing to update it, with suggestions of how. I might hope that an answer could clarify what a given study said with relation to "similar languages." Maybe study(ies) will shed meaningful light on this aspect?
    – Flimzy
    Commented Apr 5, 2016 at 17:34
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    I asked a question similar to this regarding Spanish and French. Non-related languages seem to be easier to differentiate over time, while related languages can cause conflicts that persist. Commented Apr 5, 2016 at 17:35
  • @Flimzy Spot on. If what you mean by similar is "a high level of mutual intelligibility", I might make a note in the question defining similarity. Cool question, though.
    – erip
    Commented Apr 5, 2016 at 17:38
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    In looking through some literature through my university, I'm seeing a lot on multiple language acquisition in children (specifically those in bi- or trilingual households), but not much on adult learners. Do you have a specific interest in adult learners, or in anyone?
    – tonysdg
    Commented Apr 5, 2016 at 18:36
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    – HDE 226868
    Commented Apr 5, 2016 at 22:17

5 Answers 5


According to The Polyglot Dream,

Choose two languages that are distinct from each other. Languages that are similar can overlap by way of words, grammar, emotions, memories, and other factors, thereby causing confusion. Therefore, learning Spanish AND Italian, Dutch AND German, or Portuguese AND Romanian at the same time is not a good idea.

The same source also mentions that you should restrict your learning to a maximum of only two languages, as beyond that can cause impairment in all 3 target languages. Try to choose a language that is less complex than your L1 and a language that is relatively more complex than your L1. By doing this, you can further your disassociation between both languages and thus build a stronger language core. Finally, ensure you have daily language practice in both languages.

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    How does The Polyglot Dream support these claims?
    – minseong
    Commented May 5, 2021 at 15:33

For young children learning similar languages simultaneously usually is not a problem, however for adults this could be a challenging. This mainly depends on the methodology being used, certain aspects of the languages (fundamental differences, grammar, conjugations, and sentence structure) and your own unique learning abilities. It's much more efficient if you're already bilingual or trilingual, however if you're learning multiple languages at the same time for the first time, it could be really confusing, especially when one language interferes with another (this phenomenon is called “interference”).

Interference can take place at all levels of the linguistic system, i.e. in phonology, morphology, syntax, semantics, pragmatics, and the lexicon. Here are few examples when it can occur:

  • you learn a word, but without connotation or context,
  • you pronounce sounds the way you think they look in your first language (or English),
  • you create sentences using your primary language grammar syntax.

This may happens due to dual-task interference. One study from 2009 shows that performing two tasks at the same time makes you worse at performing one or both of those tasks.

Performing two tasks simultaneously often degrades performance of one or both tasks.

So in this theory, learning two languages at the same time could potentially degrade your performance in both languages, so it's probably perform best when you focus on one task at a time.

It doesn't mean you can't learn multiple languages at the same time. It's possible to have great results, if:

  • you don't mind progressing slowly,
  • you don't get bored easily with topics,
  • you don't get frustrated while learning,
  • you are motivated and love to learn.

However if your goal is fluency, quick progress or ability to be good at one thing, rather than not bad at a lot of things, it's better if you focus on one language at a time.

Source: Can You Learn Multiple Languages at the Same Time?

Related books:

  • Crosslinguistic influence in language and cognition. Scott Jarvis and Aneta Pavlenko (2008). New York and London: Routledge. Pp 287. ISBN 0805838856.
  • Gessica De Angelis, 2007, Third or Additional Language Acquisition. Multilingual Matters, 168 pages, ISBN 13: 978-1-84769-003-6
  • New trends in crosslinguistic influence and multilingualism research. de Angelis, G. and Dewaele, Jean-Marc, eds. (2011). ISBN: 9781847694416
  • Dewaele, Jean-Marc. 2010. Multilingualism and affordances: Variation in self-perceived communicative competence and communicative anxiety in French


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    I think the connection between Hiraga et al's study on dual-task interference and learning two languages in parallel is a red herring. The study is about two motor tasks, a motor task combined with a cognitive task, and reaction time during a cognitive task (counting). This would be relevant if the question here was about learning some L2 grammar or vocabulary and some L3 grammar or vocabulary at the same time, but no one would encourage this.
    – Tsundoku
    Commented Aug 19, 2016 at 15:17
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    Since no new answer has come forth, after some deliberation I finally decided to reward kenorb's answer with the bounty, mainly because of the link to the article on 'interference' (which also has further links to relevant studies - as requested by the OP). There exists, by the way, a similar, but a bit more comprehensive article on Wikipedia.
    – J.Past
    Commented Sep 8, 2016 at 11:19
  • I do want to make the following note though: Just as we have seen a lot of discussion of learning languages simultaneously, but without taking into consideration the criterion of similarity, the above-mentioned articles talk about the effect of learning similar languages - not about the effect of learning similar languages simultaneously. In the latter context there is going to be a lot less positive transfer and a lot more negative transfer, since neither language has solidified enough in the language learner to be used as a stable basis of comparison.
    – J.Past
    Commented Sep 8, 2016 at 11:20
  • Even though I was open to any new answer, I had especially hoped that someone with comprehensive knowledge of the matter could shed some more light on this subject of interference/transfer, taking both criteria--simultaneity and similarity--into account.
    – J.Past
    Commented Sep 8, 2016 at 11:20

I found some interesting articles instead of the studies, but they should suffice.

The first article by FluentU lists five major advantages in learning multiple languages at the same time: good for your brain, saves time, similarities and differences between languages are clearer, saves you from being bored, and opens tons of opportunities.

Clearly, learning languages is excellent for your brain in so many ways... including structurally improving your brain in three months, as proven in a study within the article by Swedish and German scientists. The study has interpreters put into a three month "military boot camp" for language learning and the results were amazing:

After 90 days of intense training, the scientists, donning their spotless lab coats, came in and again measured their subjects’ brains. They discovered that their interpreters’ hippocampal regions, along with three other areas of the cortex, had grown significantly. The cortical areas increased in their thickness, indicating higher fire power for these areas of the brain.

Also, learning multiple languages can also prevent/slow down Alzheimer's disease and dementia. Learning multiple languages at a time rather than one by one is seriously less time-consuming, especially if you want to be fluent in lots of different languages. It also saves time in life and in studying time:

Imaging that you’re travelling in South America and get lost while on the way to officiate a wedding. You’re standing at an actual crossroad and looking up at two signs. The left one says “Una Via“ (One Way), the one on the right says, “Camino Cerrado Delante“ (Road Closed Ahead). Can you imagine how much driving time you’d save simply knowing what those signs mean?

One way is sequentially and the other is simultaneously. The methods are right in the names. Doing multiple languages at the same time (simultaneously) saves time because, in a way, you’re multitasking. Instead of getting fluent in one language in 1.5 years, you become fluent in 2 languages in 2 years.

You can also take advantage of the differences and similarities between similar languages, such as the romance languages. For example, you can take care of the cognates between languages like French, Italian, and Spanish (arm, fever, and tongue after proper translation):

If you notice, the spelling, meaning and pronunciation of these words (and many, many others) are similar for French, Italian and Spanish, indicating that they have a common etymology.

Cognates are very useful for 2 major things... Vocabulary building... Contextualizing.

You are not getting bored anytime soon. You might be watching Spanish shows one day then Japanese drama shows the next. Being bored will be the least of your problems if it is at all. You probably didn't know this: learning multiple languages can help you get employed, find that perfect dream guy/girl, and understand multiple different cultures:

Over the next decade, Spanish and Chinese speaking skills will be one of the most critical skills sought for by recruiters.

As globalism surges forward, it makes learning multiple languages ever more essential. English isn’t enough anymore. A great number of international corporations aren’t based in English-speaking countries. In addition, US-based corporations are waking up to the fact that in order to flourish in the emerging markets, they have to learn how to say “Ni Hao” and not just “How are you?”

On the romantic end, you’ll be ready to start a bilingual relationship. When your significant other has a different first language than you, what better way is there to express affection than learning romantic phrases in their native tongue? “Sorry” is just different when you say “lo siento.” And who knows, she might just forgive you.

Though not really a credible source, another person's insight might prove valuable, like this discussion on Duolingo (mainly the top reply):

It depends on the person. I will tell you my humble opinion, and tell how it works for me. For me, it is better to deal with multiple languages. For example, I'm learning three languages (Portuguese, Polish, German), and I'm doing well. If I have concentrated on only one language, of course I would progress faster on that language; however, concurrently learning multiple languages makes more improvement on your language knowledge in total, even if it may yield less for each language. Ah, let me explain you with an example: if I learn one language, I will proceed "6 steps" in that language everyday. Not bad. But if I learn two languages, I will move on "4 steps" everyday for each, so "8 steps" daily in total. And even more, if I learn three, I would get further "3 steps" for each, so makes "9 steps" in total. 9 > 8 > 6 . Therefore, the more languages I learn, the more total utility I get. This is my formula, and works well for me. It can be different for other people, of course.

I run an experiment myself. I found out that, I can learn and memorize an average maximum of 20 new words per day if I study just one language. On the other hand, when I learn words from two, three or four different languages, then this number can reach 35, or even 40 words in total, per day.

Also, this is not so relevant to the topic, but just I want to tell because some people have already talked about it: I believe knowing a similar language makes easier to learn the other. For instance, speaking Spanish is a significant advantage for learning Portuguese. Yes, it can be confusing sometimes (Ex: I used to write “é” (the equivalent of Spanish “es” in Portuguese) while I was doing timed practice in Spanish), but after few mistakes, you get to know your mistakes and you don't do it again. And if you know the pattern, you can easily make a Portuguese word by its Spanish equivalent without knowing the Portuguese one, and it'll mostly be correct.

Or, if a person learnt Polish and knows well the seven cases of Polish, then, when that person starts learning German, the four cases of German will be “as easy as pie” for that person, meanwhile many people are struggling and whining about those cases.

Lastly, the more you learn languages, the more your capacity of learning languages increases and the more your brain distinguishes them, consequently you commit less clashes and confusions between languages.

So every person has his/her own efficient way of learning languages. Some people can learn one language in a short time, some can learn many languages at the same time. So just find the best way for you, and learn =)

Finally, this last, not-so-related article quickly discusses some of the disadvantages of this:

Until recently, I never felt the need to learn more than one language at a time. Now that I think about it, my strict “one language only” approach was mainly for three reasons: (1) I was never in a hurry to learn languages; (2) once I chose a language, I was so involved in the learning process that I had no desire to deal with others; and (3) learning only one language at a time gave me the opportunity to polish the ones I previously learned. Now, I’ll discuss these factors in detail.

For starters, rushing through the languages is not helpful. You are going to forget them and you waste all your time learning something you learned so fast it flew past your brain... ouch:

The first six months of the learning process are the most delicate, and one needs to focus on a given language daily and dedicate to it quality work. Time is a luxury that modern men lack, so if you split it between two, three, or even four different activities, the quality of your learning will suffer. Therefore, I personally recommend learning one language at a time.

Next, learning too many at a time will prevent you from having a steady core, which disallows you to have good fluency and quick differentiating of the languages you learned, adding to confusion and question marks:

The language learning process involves the use and memorization of words, structures, and sounds; however, emotions, colors, images, and memories are also involved and contribute to what I call a “language core.” Acquiring this language core is extremely important if one wants to keep the language alive in their head, even long after not having used it. Moreover, it takes time to build a language core, so attempting to speed through the learning process with multiple languages can cause language cores to overlap, or simply prevent even one from forming.

The article also briefly discusses time management and a story to support it:

Picking up a new language doesn’t prevent one from keeping and even refining the ones he previously learned and are obviously at a higher level. The trick is having good time management skills. By trial and error, you want to find a sustainable schedule to learn languages.

In order to better illustrate what I mean by “managing one’s time,” here’s a story I call “The Two Students’ Race.” Two students (both Italian) decide to compete for a challenging and ambitious goal: learning ten foreign languages. The judges give them a ten year “time budget,” and the rest is up to them.

Student A decides that he will pick up two languages every two years. He starts by learning English and Spanish. At the end of the two years, he picks up French and German. While learning French and German, he enjoys conversing with native speakers in both English and Spanish, languages he now speaks with a certain level of fluency. He also loves reading books. By the end of the fourth year, he is relatively fluent in German and French, so he starts learning Portuguese and Swedish. At the same time, he moves to Pariswhere he gets the chance to use the four languages he learned and continue to actively learn Portuguese and Swedish. At the beginning of the sixth year, he decides to learn Mandarin and Romanian. Two years later, he finally picks up Japanese and Dutch. Then ten years later, when time is up, he speaks English, Spanish, French, and German fluently; Portuguese, Swedish, Mandarin and Romanian well; and Japanese and Dutch decently. He has weak languages, but he reached the admirable goal of building a core in more than five languages. Moreover, he will never forget these five languages. He could get rusty in them, but they will quickly come back to him.

Student B goes for the same languages, but opts for a completely different strategy—he starts learning the ten languages all at the same time. Over the years, he lacks the consistency and patience to hold onto all the languages he is learning. Sometimes he learns five, sometimes six or seven, but never ten per day. He might have brought some languages to a good level, but for the most part, his languages are at a basic level. He confuses languages such as Italian and Spanish, and Dutch and German. Many of his languages are destined to regress to a very basic level because the student did not build a linguistic core for any language.

Now, the example is a bit extreme, but it gives you the general idea. People delude themselves into thinking that doing multiple things at the same time will accelerate the learning process when, in fact, it damages the learning process. Remember the story of the tortoise and the hare? Well, be the tortoise. Patience and aiming for a long-term goal will bring you success.



  • Good for your brain

  • Saves time

  • Differences and similarities will be easier to locate

  • Won't be bored

  • Tons of opportunities are opened

  • Learn faster


  • Might rush through languages, lose knowledge

  • Might not have a good core, disallowing fluency retention and fluency itself

  • Might not be good for you time-wise

  • Pardon the long comments, but it's a long post to respond to. :) Thanks for the thorough reply. I have issue with a few of the points. First, your list of 5 benefits seems pretty subjective. "good for your brain" doesn't seem very specific, and your cited evidence for it is aobut studying a single langauge, so not really relevant to this question. "saves time" -- does it really? I can see how it would either save time, or waste time. Do you have evidence to suggest either is true (or in which situations either is true)?
    – Flimzy
    Commented Apr 18, 2016 at 16:57
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    "similarities and differences are clearer" -- Again, are they? Why would they be more clear if you learn the languages simultaneously versus in sequence? Is there evidence to suggest either method actually makes things "clearer"? "Saves you from being bored"--this one I'll accept at face value, although I have read of significant studies that changing subject matters is beneficial, but not specifically within the area of multiple languages (i.e. switching between Spanish and Mathematics is beneficial for retention).
    – Flimzy
    Commented Apr 18, 2016 at 16:57
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    Expect the length of the answer to double though... Commented Apr 18, 2016 at 18:13
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    Your answer is quite intimidating to read; you might want to remove that "wall of text" feel.
    – fi12
    Commented Apr 23, 2016 at 22:28
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    (1) TL;DR works better if used on the beginning of the long post (as header), not on the tail. (2) As Pro there is "saves time" but con is "not good time-wise" - so which one is it? Does learning two languages simultaneously saves time, or it does not? Thanks for the answer BTW. Commented Apr 26, 2018 at 20:28

EuroComRom advocates for learning all the Romance languages at the same time, when your goal is just reading -and I assume listening too-. The confusion concerns addressed by other questions becomes important when speaking and writing, but when reading it is less important to be fully aware of which exact language is it. That is in accord with my own experience: once you start reading a new romance language, it becomes like reading a different dialect of the same language.

In short: to become a passive polyglot, learning related languages at the same time may be useful. About learning to speak or write those languages, you can follow the other answers.

  • Update: I tried with three Nordic languages in Duolingo at the same time - for a few weeks and with very few writing exercises - and I can grasp something from a text in every language but I still can't tell them apart. Then, I can confirm that, from my experience, learning related languages at the same time helps understanding but probably doesn't help writing. However, doing more writing exercises could have helped.
    – Pere
    Commented Jul 21, 2020 at 19:10

I'm not sure there are any formal studies (especially a proper controlled study) that answer your question, but in this video, Professor Arguelles describes a way to simultaneously (or at least in a rapid back-to-back-to-back sequence) study Spanish, French, Italian (and German) by using a group of related learning materials. He says there is, in fact, synergy by using the same course content. The reason this is useful is because you become intimately familiar with the content. Thus, when you learn how to express certain content in one language, then it becomes easier for you in the other languages. Therefore, yes, simultaneously studying multiple related languages can facilitate immediate acquisition of another.

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