Unfortunately, as of my last update, Siri's language for web searches is tied to the device's language settings, and it might not be possible to change Siri's web search language independently from the device's language.
However, one workaround could be to ask Siri to specifically search in English by stating "Search in English" along with your query. Sometimes, specifying the language might prompt Siri to bring up results in English, although this might not work consistently.
Another option is to copy the text of your query and paste it into your Brave browser directly, set to Google search in English. This way, you can bypass Siri's web search and get results in your preferred language.