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.
There's no source that studies someone learning Japanese, Chinese, and Korean all together, but the available research on related situations — third-language learning, kanji-strategy studies, Chinese character acquisition, and multilingual education — supports a few practical conclusions: treat the writing systems as separate long-term projects, manage the anxiety that seems to build with experience in Asian-language study, be selective about memorization strategies rather than trusting the most common ones, and lean on peer/group support and deliberate cross-language connections. It's genuinely workable to study all three, but expect script learning especially to be slow and to require dedicated, separate attention for each language.
In a study of learners studying Chinese, Korean, and Vietnamese as a third language at the same time, more experience with the language was linked to higher anxiety (for Chinese) and lower grades were linked to less experience — meaning multi-language study can produce ongoing stress rather than it fading with practice, and this stress can affect performance.4
The same study found that when learners used strategies to manage their emotions (like calming self-talk or deep breathing) during Korean study, they were also better able to use vocabulary-learning strategies — suggesting that managing frustration or anxiety directly supports actually learning new words.4
Example
Learners with higher anxiety were less likely to ask questions or seek clarification about new words in class, for fear of embarrassment, while lower-anxiety learners used more active 'discovery' strategies such as asking a teacher or friend.4
A study of Persian-speaking learners of Japanese found that the memorization and mnemonic strategies people used most often for learning kanji (Chinese-derived characters) were not necessarily the ones they judged most effective, and strategy use varied by learning stage and gender.1
A study comparing multilingual and monolingual students found that the multilingual groups scored higher on tests of working memory and mental flexibility (the ability to switch attention between tasks), though the monolingual group actually had a larger vocabulary in their target second language, likely because their native language was structurally closer to it.8
In plain terms
Cross-script research emphasizes that different writing systems (like Chinese characters versus alphabetic scripts) have distinct visual, phonological, and spelling demands, so skills built in one script don't automatically transfer to a very different one.7
A study of preschoolers learning Chinese as a second language found character knowledge built up gradually across school years, with second-language learners starting far behind native speakers and only slowly narrowing the gap, especially struggling with the link between how a character looks and what it means.6
Descriptions of multilingual education programs suggest that structured peer support, small-group work, mentoring by more experienced multilingual students, and materials tailored to learners' different backgrounds are associated with better outcomes in developing communication skills across several languages at once.3
An intervention that let students freely draw on their home language while learning a target language improved learners' vocabulary confidence and self-expression, suggesting that deliberately connecting related languages rather than keeping them fully separate can help.5
In plain terms
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