Define conditionally? Are you working for international company where Chinese is less relevant or Taiwan based company? I think that makes a big difference. If it is Google in Taiwan, obvious English will be the primary communication language. However, if it is Taiwanese company, then Chinese.
I have worked in Bay Area for Taiwanese companies. Sure you can communicate in English just fine, but most of the time Chinese are spoken. Bigger decisions still relies on Chinese as main language even in the US.