Evidence-based answer · Last updated · How it’s made
There's no single "fastest" method documented for a Portuguese/English speaker learning Japanese specifically, but the sources point to a consistent set of evidence-backed accelerators: use spaced/retrieval-based practice rather than cramming for vocabulary and kanji, expect Japanese's writing system (kanji) to be the main bottleneck regardless of your native language, and lean on active strategies (context, decomposition, retrieval practice, mnemonics) rather than passive rote copying. Because English is your L2 and Japanese would be your L3, cross-linguistic transfer research suggests your English proficiency may actually help you more than Portuguese does, since transfer tends to come more from a learner's stronger/more recent foreign language than from the native tongue.
Answered for language learning in general. No specific language was set for this question, so the findings are drawn from general second-language research rather than one language’s literature.
Across studies of learners with alphabetic first languages, the Japanese/Chinese logographic writing system (kanji/hanzi) is consistently rated as the hardest part to learn, regardless of whether the learner's native language is English, Arabic, or another alphabetic language.1,9,10
In plain terms
Testing yourself on new words (retrieval practice) produces better short-term and long-term memory for foreign vocabulary than simply re-reading or re-studying word lists, based on a study of Chinese speakers learning Japanese vocabulary.3
Example
Multiple studies found that spreading vocabulary study across sessions with gaps in between (spaced practice) leads to better long-term retention than massed, one-session cramming, though the advantage shows up mainly for consciously recalled meaning rather than for the kind of automatic word-sense knowledge that develops without conscious effort.6,7
In plain terms
Example
Digital flashcard tools produced significantly bigger vocabulary gains than paper flashcards for students at basic and intermediate proficiency, while advanced students did equally well with either format.12,17
Example
Learners of Japanese and Chinese characters naturally use different strategies depending on whether they're trying to learn a character's shape, its sound, or its meaning — common approaches include using context, breaking characters into smaller components, rote writing, and listening — and these strategy preferences tend to stay fairly stable over a semester rather than shifting much.1,2
Research on learners acquiring a third language shows that influence from a person's second language can be as strong as, or stronger than, influence from their first language, especially when the second language is the one used more recently or more proficiently or is the language of instruction.5,11,14,16
In plain terms
Example
In research on learners tackling tonal or unfamiliar-sounding languages as a third language, listening comprehension is frequently under-emphasized in instruction compared to speaking and writing, even though processing unfamiliar sounds is cognitively demanding and important for real communication.13
Learning vocabulary through emotionally engaging, immersive methods (such as virtual reality scenes or storytelling projects) can improve retention, with personal factors like self-perception and empathy affecting how much benefit a learner gets.4,15
Example
Watching Japanese anime informally motivated many non-native speakers to become interested in and begin learning Japanese vocabulary and culture, even without formal coursework, though this research measured interest and informal learning habits rather than proving anime-watching alone leads to fluency.8
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