I’m not sure that East Asian languages can fit into the same language family block. You couldn’t very easily go from learning Korean, where the writing has an alphabet system, to learning traditional Chinese, where one part of the pictogram decides meaning and another decides sound — and in some cases the sound and meaning are completely segregated.
Even languages within the East Asian bloc which use the exact same writing system, like Mandarin and Cantonese, are difficult. Spoken mandarin only has 4 tones, while Cantonese has 6. Many native mandarin speakers can understand Cantonese but really struggle with speaking.
This is also difficult with some Southeast Asian languages which have been heavily influenced by colonialism, like Vietnamese (French influence) and Indonesian (Dutch influence).