This is called linguist relativity (nee. The Sapir-Whorf hypothesis) and the strong form you describe has fallen out of favour in modern linguistics.
A surprising number of monolingual people think their own language is the most adaptable and modern language, but this is obviously untrue. All languages evolve to fit the needs of speakers.
Also, the idea that people "think in language X" is heavily disputed. One obvious counterargument is that most people have experienced the feeling of being unable to express what they are thinking into words -- if you truly did think in the language you speak, how could this situation happen? My personal experience is that I do not actively hear any language in my head while unless I actively try to think about it (at least, since I was a teenager).
(This is all ignoring the comments about ESL speakers that I struggle to read as anything but racism. As someone who speaks multiple languages, it astounds me how many people seem to think that struggling to express something in your non-native language means that you're struggling to think and are therefore stupid.)