Japan has opened its first osmotic power plant – so what is it and how does it work?
(www.theguardian.com)
i recognize you probably have no racist intention.
non-English speakers and bilingual English speakers, including those who speak Asian languages, often experience that type of mocking of their language. if it happened once to one person in the history of earth, it's not racist. but the collective effect over generations and across thousands of experiences creates accumulative pressure on specific identity groups of people. the pressure and related coping/denial behaviors can manifest in unpredictable and inconsistent ways which may be why not everyone understands that racial mocking causes measurable harm.
tl;dr
it really helps if you would not do that. even more so if you could help stop others who you observe doing the same.