Unfortunately for Americans, fluency in a second language is something only enjoyed by a select few. Either you grew up in a home where English shacked up with a mother tongue, or you found the discipline to master a new language through practice. For the rest of us, English is all we’ve known and all we’ll ever get.

That’s not to say some languages aren’t easier to pick up than others. Assuming we get the urge to learn more about a culture or make a pact to travel like a native, which means talking the talk, we can fold in a new way of speaking, and indeed, thinking. The trick is knowing what to expect. Some languages sound like English — just a little…off, while others might as well be indecipherable codes intercepted by warring countries. How does science explain that difference?

Apples And Oranges

Linguists like to pick things apart, so we can think of languages as being made up of three basic components: the phonology (how words and letters sound), the grammar (how those sounds are organized in a sentence), and the words themselves (how ideas and objects are represented verbally).

For English speakers, who operate with 44 producible sounds (known as “phonemes”), sentences that flow from subject to verb to object, and over a million words made up of 26 letters of the Latin alphabet, the basic challenge in learning a new language is staying as close as possible to those three benchmarks. Some accomplish the goal much more easily than others.

Spanish, for instance, is widely regarded as a natural second language for English speakers. With its 24 easy-to-pronounce phonemes, subject-object-verb grammar structures, and only one additional letter — ñ — many English speakers find Spanish a quick pick-up. Mandarin, meanwhile, is much harder. While it does use fewer phonemes than English and is generally thought to use a simpler grammar structure, it relies on tones to impart meaning, which English doesn’t employ, and instead of 26 letters to form words it uses thousands of representative characters.

Nuria Sagarra, associate professor of psycholinguistics at Rutgers University, also argues morphology — a language’s structure, based on parts of speech — plays a presiding role. English, for example, has a poor morphology, Sagarra explains. We need more than the verb “slept” to know who did the sleeping. But in Spanish — and other languages with richer morphologies — the subject is embedded in the verb: durmió, or “he slept.”

What makes one language harder to learn than another, Sagarra says, is how experienced the learner is with transferring between linguistically complex structures. That ability tends to arrive at intermediate proficiency, she told Medical Daily in an email.

“If your native language is more similar to the foreign language (e.g., your native language has rich morphology and you are learning a rich morphology, such as a Russian learning Spanish), things will be easier.”

It also doesn’t hurt to have a good memory, she says.

How Can We Know?

It’s tempting to say earning an A on a Spanish test means a person is moving toward fluency, but based on Sagarra’s experiments, she says, “this is far from real.” Learning languages is hard because it requires brand new cognitive frameworks. Simply translating the new structures through the filter of a native language isn’t learning. It’s memorizing.

For people like Sagarra who study the way our brains make sense of new languages, the challenge is figuring out when learning actually takes place. When is the brain playing by the new rules? In 2013, Sagarra and her colleague Nick Ellis, of the University of Michigan, found through eye-tracking technology that people’s proficiency level determines where they spend their time concentrating. In that particular study, the investigators focused on adverb-verb congruency (“Yesterday the man eats” versus “Yesterday the man ate”) among English and Romanian learners of Spanish.

They discovered people read the Spanish sentences in line with the structures of their native language. As people got more proficient, their transfer rates increased, until a point when they knew the language well enough that their new frameworks supported the learning without needing to go back and forth.

Unfortunately, there aren’t in-depth studies that compare each language on these grounds. The best linguists can do is draw out some principles about language complexity and deduce which languages might be difficult for which native speakers.

Romance languages tend toward the top, often joined by Dutch, Swedish, and Norwegian. A little more time-consuming are Asian and Eastern European languages, which make use of different morphological elements: Hindi, Thai, Greek, Finnish, and Turkish. Then come the heavy-hitters, such as Mandarin, Arabic, Farsi, and Korean, which look and sound completely different than English.

It Gets Better

Luckily, the road ahead for language learners seems to get smoother with time. As you accumulate more languages in your arsenal, you gain an ability to transfer new languages through smarter filters. Success breeds success. If you already know Japanese and want to learn Mandarin, for example, you’ll probably have an easier time than someone who just knows English. Instead of transferring the new language through English, which stands at the opposite end of the morphological spectrum, you can use the frameworks for Japanese instead.

With that in mind, where you learn could end up making all the difference. Research has repeatedly found the immersive experience of language learning can’t be recreated in a classroom. If people have any hope of securing bilingual status — adopting all the nuances of everyday speak, not simply the stale phrases found in a textbook — they need to dive in headfirst.

The net effect of this is a brain that is forever more complex. People who speak more than one language exercise more executive control, mental flexibility, and concept formation. In this, Sagarra offers a word of advice to parents thinking of raising their kids bilingual.

“Bilingual kids need more time to talk and some teachers suggest parents to raise them monolinguals,” she said, “but bilinguals kids catch up at the end, so it's better to be patient and wait.”