(US native speaker)

As far as I know, there are no other languages that an English speaker can understand without studying.

The language closest to English is said to be Frisian, but English speakers can't understand Frisian at all. Here's an example:

<em style="color: rgb(34, 34, 34);">Die Wänt strookede dät Wucht uum ju Keeuwe un oapede hier ap do Sooken.</em>

I got that example from https://en.wikipedia.org/wiki/Frisian_languages

<em>#Dan So what is your native language? </em>English, US native speaker.

All English speakers will recognise the rhyme and stresses of this language, there will be words that they can easily guess.

Dating from a time when you could wade from parts of the Frisian coast in western Europe to the English coast.

Turn on the closed captioning on youtube to see the English.

Supposedly it’s closest to Dutch or Ostfriesisch but it’s a pretty tough call. Hard to match it with anything really. Not like Portuguese or Spanish.

"There is no other language, for example, that is close enough to English that we can get about half of what people are saying without training and the rest with only modest effort. German and Dutch are like that, as are Spanish and Portuguese, or Thai and Lao. The closest an Anglophone can get is with the obscure Northern European language called Frisian: if you know that tsiis is cheese and Frysk is Frisian, then it isn’t hard to figure out what this means: <em>Brea, bûter, en griene tsiis is goed Ingelsk en goed Frysk</em>. But that sentence is a cooked one, and overall, we tend to find that Frisian seems more like German, which it is."