No second language? You can still apply for a Fulbright
You don’t have to speak a second language to apply for the Fulbright US Student Program. What’s imperative is that you are able to conduct your study or research with the skills--research or otherwise--that you have. Here is a list of countries where you can propose to undertake a Fulbright research project in English.
A second language more than doubles the number of possible host countries you can propose, but if you don’t have skills in a non-English language, and your project can be successfully completed without second-language skills, the project proposal will be fully considered in the application process. You can only apply for one Fulbright US Student Program award at a time, to a single host country,* anyway.
The Fulbright selection committee is looking for you to demonstrate that you can do your project, not for you to be fluent in a second language. There are many people who do artistic or scientific Fulbrights successfully without second language skills, and many more across many fields who both apply and complete Fulbrights with elementary to intermediate levels of language proficiency.
Lacking a second language, however, should not be what determines your host country: proposing the UK or Australia because you think they’d be nice places to visit and you don’t speak another language is a fast-track to rejection. If you propose a particular host country, it should be because you are genuinely interested in that country and your project is relevant and doable in that country.
In another post, we address how possibilities open up when you speak even a little bit of another language, and how you can use the time between now and when you submit your application to improve your language skills.
*There are a couple of regional programs that allow multiple countries, but it’s still one Fulbright, and you can only apply once in the application cycle.