The ideal age to start learning a foreign language is an issue that has been debated by 言語学者 (gengogakusha, linguists) for decades. According to the critical period hypothesis, which was first put forward by Wilder Penfield in 1959, a second language can only be fully mastered by those who begin studying it before reaching 思春期 (shishunki, puberty). Many scholars and language learners have since dismissed this as nonsense, yet it’s still a theory that is widely accepted around the world.

Japanese actress Yuho Yamashita — who has appeared in a number of German- and English-language films and dramas, including “Der Alte” (“The Old Man”) and “The Forest,” alongside Natalie Dormer — believes “there’s an element of truth to Penfield’s assertion,” particularly when it comes to 訛り (namari, accent).

“I think to sound like a native speaker you need to start seriously learning a language before the age of 14,” she explains. “I know that I’ll never sound perfect in either German or English because I started too late with both. All I can do is work as hard as I can to make my speech in the two languages as clear as possible.”

The 31-year-old got her first big break as a 子役 (koyaku, child actor) in the stage production of “Annie” at 11, and followed that up by starring in 甘辛しゃん (“Amakarashan”), an epic NHK 朝ドラ (asadora, morning drama). She began studying English in her teens and then moved on to German at university because at that time her dream was to work in the 環境分野 (kankyō bunya, environmental sector) and Freiburg was considered the most 生態系に優しい (seitaikei ni yasashii, eco-friendly) city on Earth. After living briefly in Freiburg, she moved to Berlin, and she now calls Leipzig home.

As far as I can tell, she is かなり流暢 (kanari ryūchō, fairly fluent) in both English and German. During our interview — conducted in English — she occasionally mixes up some vocabulary and speaks with a bit of an accent, but in general is easy to understand and has little trouble getting her point across in a 簡潔 (kanketsu, succinct) manner.

“The most important thing as an actress is that you’re understood,” she says. “I spend a lot of time listening to rhythm and intonation. I also did phonetics classes in both languages, using different muscles to try and imitate native speakers.

“I know I don’t sound perfect, but that’s OK because I’m Japanese. When directors cast me, they aren’t looking for a pure German or Brit. That’s not to say I don’t want to get to that level — if you learn a language you should always strive to be the best you can be — I just think it’s important to realize there are limitations.”

Of course, not all adult language learners think like that. The desire to be native-level is overpowering for some, which can lead to demotivation and 挫折感 (zasetsukan, a feeling of frustration) if they aren’t 完璧 (kanpeki, flawless). Temple University professor Aneta Pavlenko believes this is one of the main factors that stops people learning languages efficiently, describing it as “an unreachable standard that looms over us.”

Linguists Murray J. Munro and Tracey Derwing agree. They feel when it comes to the study of 発音 (hatsuon, pronunciation), too much emphasis is placed on achieving a “textbook-perfect accent,” when in fact it should be learned with the goal of communicating easily with others. As they say, “Even heavily accented speech can be highly comprehensible.”

Hollywood stars like Arnold Schwarzenegger, Antonio Banderas and Penelope Cruz are 適切な事例 (tekisetsu-na jirei, cases in point). They started learning English relatively late in life and subsequently none of them sounds American, yet this hasn’t hampered their acting careers in the U.S.

Despite speaking with “foreign accents,” audiences can still understand what they’re saying and きっとそれが重要なことだ (Kitto sore ga jūyō-na koto da, “Surely that’s all that matters”). It’s certainly what Yamashita cares most about, though getting to that level in English hasn’t been easy.

“I personally found it too confusing to study two languages at the same time, so for a number of years I focused entirely on German and shut English out,” she says. “In 2013 I had some auditions in London, but quickly realized I couldn’t communicate properly with casting directors there so I decided to go to The Actors’ Centre in Covent Garden to try and brush up my English. I think because I was so highly motivated to improve, I was able to get roles in American films like ‘Take Down’ and ‘The Forest.’ Then when Natalie Dormer said I was doing great, I felt even more confident.”

For adult learners of a second language like Yamashita, 動機づけ (dōkizuke, motivation) is the key. Whether it be 内的 (naiteki, intrinsic) or 外発的 (gaihatsuteki, extrinsic), we all need that purpose or goal to keep pushing us to the next level. Even if a native-like accent proves difficult, fluency is attainable for anyone determined enough to reach their objectives, and not just those who start studying when they’re children, despite what the critical period hypothesis suggests.