Yes, but it costs time and invites mix-ups. Each language needs its own large dose of input, so two at once roughly halves what each one gets. Research on learning a third language suggests that closely related languages, and languages you know only a little, are the likeliest to leak into each other.
Will the two languages get mixed up?
Sometimes, and it's partly predictable which ones. Research on learning several languages is still limited, and we found little on adults starting two at the same moment. But there is a body of work on people learning a third language after a second one, and it shows when one language bleeds into another. Williams and Hammarberg (1998) proposed four factors that decide which language a learner borrows from.
| Factor | The idea | What studies found |
|---|---|---|
| Typology | A closely related language is more likely to leak in | Supported in several studies, though rarely as the only factor: a Romance second language influenced a Romance third language more than a Germanic one did (Lindqvist & Bardel, 2014) |
| L2 status | Learners reach for another foreign language rather than their mother tongue | In one study of learners of Swedish, function words and word order were borrowed almost only from a previously learned foreign language, while content words came from both |
| Proficiency | How well you know the other language | Mixed: some studies find a strong language leaks more, others a weak one. In Falk & Lindqvist's 2023 case study, foreign languages known at C1 or above weren't transferred, but weaker ones were |
| Recency | The language you used most recently leaks in | Little support: a study of 41 learners of Dutch found recency played no role |
Borrowing is also strongest at the start: the same review notes that influence from an earlier foreign language tends to fade as you get better at the new one. Put together, the riskiest combination is two closely related languages that you are both just beginning.
How much do related languages overlap?
A lot, which is both the help and the danger. We took the 200 most common lower-case word forms in the free chapters of each language and counted how many appear, spelled exactly the same, in the free chapters of another.
| Language pair | Top 200 forms shared |
|---|---|
| Danish → Norwegian | 127 |
| Swedish → Norwegian | 77 |
| Swedish → Danish | 66 |
| Russian → Ukrainian | 63 |
| Spanish → Portuguese | 62 |
| Spanish → Italian | 37 |
| Italian → French | 30 |
| Spanish → French | 23 |
| Dutch → German | 21 |
| Spanish → German | 4 |
Many more words differ by a letter or two. The Spanish and Italian versions of the same A1 story introduce their heroines almost identically:
Lucía es tímida y lleva un cuaderno en la mano.
Elena è timida.
Is it a good use of your time?
Only if you have the hours. The US Foreign Service Institute's estimates for English speakers show how much each language takes on its own, with 23 hours of class and about 17 of self-study a week.
| FSI category | Examples | Typical course length |
|---|---|---|
| I | Danish, Dutch, Italian, Norwegian, Portuguese, Swedish (24 weeks); French, Spanish (30 weeks) | 552–690 class hours |
| II | German | About 828 class hours |
| III | Polish, Russian, Turkish, Ukrainian | About 1,012 class hours |
| IV | Japanese, Korean, Mandarin | About 2,200 class hours |
Two languages mean roughly the sum of both. Reading volume splits too: Paul Nation suggests a learner with about 1,000 words reads at least 10,000 words a week, and that target applies to each language separately. Our page on extensive reading explains why the volume matters.
How do you learn two languages at once, if you want to?
- Stagger them. Get one to a comfortable level first. Contos treats 1,500 known words as the start of B1; at that point the first language is far less fragile.
- Pick languages that are far apart. Related languages are the likeliest to interfere, so Spanish with Japanese should cause fewer mix-ups than Spanish with Portuguese.
- Give each its own slot. Tie each language to a different daily cue; see building a daily habit.
- Expect the related pair to help your reading first. Overlap makes texts easier to follow long before it makes speaking easier to keep apart.
Read a chapter 1 in the language that matters most to you, and give that one your first slot each day.
Read free in your browserFrequently asked questions
Should I learn Spanish and Portuguese at the same time?
It's the classic hard case. In our count, 62 of the 200 most common Spanish word forms appear identically in Portuguese, and many more differ slightly. That helps reading but makes mixing likely when you speak. Most learners find it easier to get one to an intermediate level first.
Does knowing one foreign language make the next one easier?
Often, especially if they're related: you recognise words and structures. The Foreign Service Institute lists prior language-learning experience among the factors that affect how long a language takes. The same overlap is also the main source of mix-ups.
How many hours a week do I need for two languages?
There's no fixed figure, but each language needs its own time. Foreign Service Institute courses run at about 40 hours a week for one language. Most self-taught learners have far less, so two languages at once usually means slower progress in each.
Why do I use words from my first foreign language in my second?
It's a known effect. Research on third-language learning finds learners borrow from an earlier foreign language, especially a related one and especially at the start. It usually fades as the new language grows.