Thinking in another language is the hallmark of true fluency, vs having to auto-translate in your head how to say something before you say it. So the entire argument around people employing "more careful and deliberative thinking when using their foreign language," tells me the sample people were not likely fluent speakers of another language.

They may have studied for years and gained strong proficiency - but that is not the same thing as fluency. Once you reach the state of true fluency you are not second guessing yourself all day long about how to say what you want to say -- you just say it. You can switch thinking from one language to another, and it's fairly unconscious.

People who speak several languages fluently also tend to have a strong awareness of cultural norms associated with speakers of those languages. When you straddle different cultures, you start seeing and thinking about a lot of things differently.

If the studies were meant to augment already established science on the impact of foreign language study and acquisition in adults, they should be clarifying at what level of acquisition the sample rests.