I was fascinated by this paragraph because it, in some ways, parallels how my proficiency in languages has shifted with each new life experience.

I grew up in Penang, where Hokkien is the lingua franca, although I spoke Cantonese with my grandparents at home. So, both of these dialects still exist somewhere in my "mental lexicon" (can't think of a single word to describe all the words I know in all languages, so this will have to do). As I spent more years in Kuala Lumpur than in Penang, my Cantonese has improved to the relative detriment of my Hokkien. Malay's always been in the background since that's what I spent hours learning in school, but English is the language in which I consider myself a native speaker.

Now that I've been living in Bangkok for six months, though, an emerging awareness of the Thai language is happening. It feels that my mental lexicon is expanding, but the growing Thai knowledge is happening at the expense of my Hokkien and Cantonese. Meanwhile, Malay is stable, while the English is still growing slowly - but that's because I'm exercising the English writing muscle consistently.

What I'm hypothesizing is there's a base level of proficiency, above which one's language skills is protected against the incursion of a new language. Below that, it gets muscled out by the new language.

Or maybe the different tones of the Thai language interfere most with other tonal languages, like Hokkien and Cantonese.

Thanks for your thought-provoking article, Alvin!