Another generally good approach: Avoid big words if you can. Uncommon words are much harder for non native speakers to comprehend even if we know the word. Often I found myself searching in my memory for the word's meaning and missed a whole sentence. It's difficult to do if these words permeate the materials you engage with，but not impossible. Also，don't use the word permeate!
As a Chinese national currently living in the west, I think I broadly agree with your argument that "efforts to expand effective altruism into other languages should initially focus on person-to-person outreach to a small number of people with key expertise." I also appreciate your grasp of the complexity of cultural and linguistic barriers in promoting EA ideas in the Chinese context, which can often be lost on EAs who are less familiar with other cultures.
One potential objection to this is that not rushing into massive translation effort does not equal to not at least attempt some translation at all. A set of core materials can still be useful, if it is carefully curated by professional translators (not merely bilingual volunteers like me). Without written material, it can be difficult to make ideas stick, even among a small group of personal contacts. A counter argument to this, however, is that the initial promising groups are very likely elite college students and urban professionals who would have no problem reading English materials. I don't have a strong opinion on this.
Another potential problem I can foresee regarding 'personal contact' approach is that to my knowledge, the Chinese government keeps close tabs on any recruitment activities by foreign social movements. Anecdotes from missionary friends 10 years ago suggest that their religious activities, especially when involving locals, were closely monitored by the police, kept under 20 people, and sometimes harassed. I cannot speak with any confidence that this is still the case, or if it will be applied to EAs equally. But this is something to keep in mind when evaluating personal outreach versus media effort.